It's fun to discover new lightweight applications. They work well on newer computer systems as well as older or slower computers and low resource machines like many mobile devices. You can run more of them at once. If they're not well-known, they can actually be more secure sometimes (using the security through obscurity principle). I also personally prefer portable applications. That way, you can use the same programs on any operating system. You don't have to relearn new programs for each system you work with.

It can be quite a challenge to find new lightweight applications. I've read several threads on forums where users post their favorite lightweight applications. Many truly are not lightweight by standards that take into consideration memory usage, lines of code, compilation time and/or number of dependencies (libraries).

One way to find lightweight applications is to look for programs built with lightweight GUIs. I've seen a few comparisons of GUI performance. This one is particularly good because it tests the various GUIs and gives statistics:
I was rather surprised by the SDL2 results. Generally, the time it takes to build a GUI from source is one good indication of complexity. FLTK and SDL both build quickly from source compared to the other GUI frameworks mentioned. So, I was surprised that SDL2 scored so badly on the memory usage tests. I'd be curious to know if SDL 1.2.x (which many systems still use) would show a large improvement. Another surprise was how well Tcl/Tk did in the tests. I typically think interpreted languages have worse performance than compiled ones. It would be interesting to see some statistics on response times for similar applications created with these GUIs.

I often go through various source repositories such as Sourceforge, github, etc. looking for code written using specific user interfaces in order to find new and interesting applications. Standard search engines are another way to search for programs. The user interfaces I'm personally most interested in at this point are FLTK, pdcurses/ncurses, SDL and command line programs. These types of applications are typically more lightweight or designed to do one thing well. Know of any other lightweight GUIs or TUIs (text user interfaces)? Please share your recommendations and why you like them.

There are some nice blogs for finding and discussing minimalistic (or in some cases maximalistic) programs. Unfortunately, many are no longer very active. Some favorites are:

If you know of others, I'd love to hear about them.

One can also look for lightweight distributions and see what programs they have in their repositories or read their forums for more suggestions. Some of the interesting distributions to check are TinyCore Linux (uses several FLTK programs), Nanolinux (uses more interesting FLTK programs), Rogue Class Linux (uses several SDL programs), Puppy Linux, AntiX (Debian based), INX ( ), Absolute Linux (Slackware based), 4MLinux ( ), OLPC. Typically DSL and Puppy get mentioned when people list lightweight Open Source systems. There's been no active development on DSL in a long time and the forums are very quiet. I also found Puppy a little too resource intensive on one of my older machines. FreeBSD performed much better on that system. Puppy Linux has some interesting discussions in their forums.

Linux systems that work in framebuffer mode using DirectFB, nano-x and other alternatives also typically contain many interesting, unusual and lightweight applications. Nanolinux and Rogue Class Linux are in this category.

One can also look at operating systems and development projects that use more lightweight C libraries (such as uclibc and musl). Those projects typically gravitate to choosing lightweight applications, command line and console based programs and lightweight tools like Busybox and Toybox.

Alternative operating systems often offer interesting lightweight application choices. Syllable and Haiku often use SDL programs and other lightweight applications that are easier to port to those systems. Systems like Minix and ELKS are also interesting to investigate. Minix 3 uses a lot of the programs that BSD systems do, but earlier versions of Minix include some interesting alternatives. XFDOS includes many interesting FLTK applications. Plan 9 is interesting as well, but not many of the programs used on this system have been ported to other systems. Another good place to look for unusual applications is on mobile devices.
Here are some application lists from Syllable and Agenda:

I'd love to find more places to discuss lightweight applications. If you've written an article on the topic, please share it. If you know of a good blog, forum, mailing list or other resource, please let me know ( ). If you'd like to discuss your favorite C/C++ applications further, you're welcome to use the CppDesign mailing list ( ) as a forum.
Some interesting Open Source command line programs output their results in Postscript and/or PDF format. That makes it useful to have lightweight PDF and PostScript viewers that don't require a lot of dependencies to build so you can view their output quickly. It's also nice on Linux systems if they work in framebuffer mode, so you don't have to start an X Windows session just to view results. Cross-platform viewers work on a variety of systems from Linux and Mac to Windows to DOS and even Android. Having tools to edit/modify PDF and PostScript output is also useful.

I've been searching a lot lately for lightweight PostScript and PDF viewer options. Thought I'd share some of what I've learned about cross-platform PostScript and PDF support. If you know of any other viewers or PDF/PostScript related programs with minimal build dependencies that I may have missed, please let me know. I'm always looking for additions for my Open Source applications list:

First, here some of the programs I use that output to PDF or PostScript.

This does have a lot of build dependencies (needs Qt and webkit), but it's one of the few programs that I've been able to find that does a good job of converting HTML to PDF.

Other HTML to PostScript/PDF alternatives are html2ps ( ) which requires Perl and PhantomJS ( ).

I use abcm2ps to convert songs in ABC notation to sheet music. Later versions of abcm2ps have the ability to output to SVG as well as PostScript. I have a lightweight SVG viewer based on nanosvg and SDL that displays SVG, so that should be an interesting display option if a PostScript viewer isn't readily available. I can upload the build scripts for it to my archive if anyone wants to try out the SVG viewer.

lcal and pcal
Personal calendars and lunar calendars can also be output to PostScript format.

The graphics layout engine outputs charts and graphs to PostScript, PDF and some graphics formats.

Other applications can output starcharts, barcodes, graphs, etc. to PostScript format. The applications I listed above are the ones I personally use the most in this category. If you have other favorites, would be interested to hear about them.

Next, I'll mention some PDF libraries and viewers.

The two main PDF rendering libraries/applications are mupdf and poppler.

Poppler is a library based on the xpdf viewer, so in most cases you really only need one of these on your system. They both have a lot of the same utility programs. When building poppler, there's additional support for GTK and Qt frameworks if you have those on your system. I typically build with these turned off to lower dependencies.

Mupdf was written by the developers of Ghostscript. It renders very quickly and is supposed to be very lightweight. However, what I dislike about it is its growing list of dependencies. Newer versions of mupdf provide more and more functionality, but they're requiring more dependencies to do so. Later versions of mupdf now require harfbuzz which I typically don't use with any other applications. (I'm not using Opentype fonts.) Also, the developers recommend you use their third party libraries rather than system libraries. There are work-arounds to use the system libraries, but it's a nuisance to modify the build scripts each time the program is updated. The API is not very stable either. Every time I download a new version, it seems to break third party utilities built using the mupdf library.

Mupdf has example viewers that come with it. The latest example includes an OpenGL based viewer. I did some work on a SDL based viewer using mupdf, but the API kept changing, making it difficult to maintain. When the OpenGL based viewer was added, I looked into using picogl in place of OpenGL/Mesa as a backend for the viewer. Using a viewer that comes with mupdf meant the mupdf developers would be responsible for dealing with the API changes. I got the OpenGL based viewer to build with picogl, but picogl still needs additional functionality to provide clear rendering of the text displayed by the mupdf viewer. Hope to work on this further in the future and would love to hear from anyone else who'd be interested in helping on this project.

There are some SDL and framebuffer based PDF viewers. However, they were either not easy to port to other platforms or had heavy dependencies I didn't want to add to my system. I found it interesting that some viewers used SDL as the actual graphical user interface (and could run in framebuffer mode on Linux), but still required GTK or Qt as an additional interface when rendering pages.

I finally found a lightweight, cross-platform PDF viewer that uses FLTK as a front end. It's called SpRead ( ). It can be run in framebuffer on Linux using FLTK built with nano-x. The viewer is very lightweight and does seem to render quickly. Dependencies are really minimal compared to other viewers I've looked at. However, mupdf renders faster in many cases. SpRead uses poppler for PDF rendering and libarchive for zipped/archived file access.

Some other interesting PDF libraries available for editing and creating PDFs are qpdf ( ) and libharu ( ).

Poppler and xpdf both come with PDF to text conversion utilities. This is very useful if you want to work with grep to search for a word or phrase in a collection of PDF files. Mupdf has added the ability to convert to text in more recent versions. However, their help/man pages on how to use their tools could use improvement. When I was searching for a lightweight PDF to text converter, I ran across pdftxt at As I mentioned, the mupdf library API keeps changing with newer releases, so typically when I update my version of mupdf, the pdftxt build breaks. I've uploaded patches to build pdftxt with the version of mupdf that I've most recently updated to. You can find patches and build scripts at the archive link on this page:

Since lightweight PDF viewers are more plentiful than PostScript viewers, I searched for PostScript to PDF converters. The main option in this category is Ghostscript. Like mupdf, it requires several dependencies and uses its own versions rather than system versions of libraries. It's actually worse in this area than mupdf. The only viable option to Ghostscript that I could find for PostScript rendering was xpost ( ). It has less dependencies that Ghostscript and is easier to build. However, it's still a work in progress. I'm hoping at some point that it will replace Ghostscript for the functionality I'm interested in, but it at this point, it still doesn't have all the functionality I require. It does look like a promising project though.

Those are some of the interesting libraries and applications I've found on my search for PostScript and PDF related utilities. Hope you find some of them useful. If you know of other lightweight, cross-platform alternatives, I'd love to hear from you about them.
I covered SDL based applications. Now, I'd like to cover FLTK based applications for desktops and/or productivity.

While there isn't as much FLTK application development going on as I would like, there are some projects that specialize in using FLTK. TinyCore Linux is probably the most well-known Linux project that uses several FLTK applications. Nanolinux is based on TinyCore but uses nano-x as a lightweight alternative to X Windows. The developer of NanoLinux uses mainly FLTK applications and has modified and updated several FLTK applications to give them new life. He's also created some of his own where good alternatives did not exist. The Equinox Desktop Environment also uses FLTK, but it typically requires another EDE specific library along with FLTK support. Also, EDE users don't always look for FLTK applications for their desktops. Some will typically use anything they consider lightweight (whether it really is lightweight or not). A few mobile devices use FLTK as their main GUI. Users of those systems have developed some interesting applications for their devices.

There are several versions of FLTK. Applications may work with one version and not another. I've spent a lot of time searching for applications and porting applications to the latest version. I did try to update the FLTK software links list at the official FLTK web site with information on what worked with the latest version of FLTK and with information on newer FLTK applications, but was unable to add some of the newer, more interesting FLTK applications out there. So, this is my definitive list at this point in time of the best FLTK applications available. For more information on FLTK and applications, see also

I'm sure I haven't covered everything and as mentioned, check NanoLinux and Tiny Core Linux for more FLTK based applications. I'm always looking for new, portable, lightweight FLTK based applications. If you know of something I may have missed or you're working on a new FLTK based project, please contact me.


Shows disk usage. Works on POSIX systems with du command. I have patches to port this to Windows.

Calculator. The FLTK web site link includes information on some of my patches to get it to build successfully as well as link to the original source code.

Graphical diff program.

Traverse directories and find file differences. Some of it was based on fldiff.

Password manager. I ported this to work with the latest versions of FLTK and tinyxml2. It's interesting, but at this point, I'd prefer a Keepass compatible password manager. I'm looking into chkpass as a lightweight alternative for password management.


prozgui for prozilla
Fast file downloader. I have patches for building and to port this to Windows. I use a version based on GNU GPLv2 development instead of the GNU GPLv3 development.

IRC client. Based on MegaIRC, but with a lot of cleanup. I have patches to add gettext/libintl support. This is the best option for IRC using FLTK that I've found to date.

This has good potential as a threaded IRC client. It can handle multiple connections. I could get it to build on Windows either with patches or a build of MinGW with POSIX instead of Windows native threading support. It needs some work on storing IRC connections. Doesn't seem to remember any connections once you leave the application.


There are two webkit based browsers for FLTK. That's great news for FLTK applications users. What's not so great is that they don't port well to non-POSIX systems. If you want the most lightweight webkit based browser (and webkit browsers are not by nature lightweight), I'd go with either of these options instead of the many other webkit ports out there.

I was able to get the original version of netrider to port to Windows and a Windows version of it is available at Sourceforge. However, when I upgraded the version of my MinGW compiler, I was no longer able to build netrider. Seems the webkit developers took some shortcuts in the older code that really weren't up to C++ standards. Netrider upgraded to a later version of webkit (which fixed the compiler issue), but the newer version was never ported to Windows.

This was never ported to Windows although it might be easier to port that the latest version of Netrider. It uses makefiles created by the developer instead of cmake.

When people talk about FLTK based web browsers, Dillo always comes up. However, Dillo is the opposite of what I think of when I think about portable code. One developer decided to fork Dillo and make it more structured and easier to port. He's really done a wonderful job on cleaning up the code. I'd recommend this browser over Dillo if you're interested in doing anything with the source code or need a lightweight HTML viewer for FLTK. DPlus is also the lightest browser I could find that could display output from diffh properly. Most console browsers like lynx had trouble rendering the color differences in the output.

While this is meant as a utility rather than a web browser, I used DPlus as the starting point for my HTML/CSS based dialog replacement.

Mail clients

The developer of Nanolinux wrote a nice, basic, stable e-mail client. (He also reused part of my Open Source POP3 e-mail code.)

This has a lot of potential. It took a long while to get it to build with the latest version of FLTK and it's still kind of buggy. I also needed to update helper libraries fl_toggletree and fleditor to work with the latest FLTK. The interface is a lot of like sylpheed and foxmail. I would love to see some new development on this and would be happy to help update it.

There was a nice, very basic, stable e-mail client at Sourceforge. Doesn't appear to be available from there any longer.

RSS reader
Gautier's RSS reader
This one has a lot of potential. It has an attractive user interface that's easy to work with. However, it does have the ability to sort RSS posts at this point at time. It needs to be used in conjunction with a script and tools like curl to download the RSS feeds. It's basically just a reader. It uses SQLLite to store the RSS data so it can potentially provide fast access to RSS posts. I'd love to see some further development done on this project.


Cross-platform VLC based media player.

Unfortunately, this only works on POSIX systems so far. I have been able to build it on Cygwin as well as BSD and several Linux systems. This might be portable to more platforms using nano-x (and possibly SDL as the backend for nano-x), but I did not get very far in investigating this option. It is my favorite xine front end and is more lightweight than many of the other xine front end options. It provides a variety of features including a nice visualization component for use while playing music.


Simple Audio recorder and player based on Sox. I have done some work to port this one to Windows.

Midi keyboard.

Audio effects program to stretch sounds.

After more than one try to get this to build with the latest version of FLTK, I finally managed to get this working. It's a nice, lightweight audio editor. It doesn't display multiple tracks like Audacity. It does not have good support for playing or recording wave files. It's basically just a wave file editor. Was considering using libsox or another Open Source sound library to add support for playing wave files.

There is a fork of FLTK called NTK. It isn't as portable as FLTK and requires POSIX/X Windows support. A suite of audio applications were created with it.


This is a great, lightweight graphics editor. I really like this one.

Specialized graphics editor for coloring old photos.

Other graphics and drawing options include Antipaint and Cinepaint. Antipaint was updated to work with the lastest version of FLTK and to improve portability by the developer of Nanolinux. You'll find it at the Nanolinux web site. At one point Cinepaint decided to port their project from GTK to FLTK. You'll find some older versions with some FLTK support and utilities. However, the FLTK port is not actively developed.


The Daily Journal is a Personal Information Manager (PIM). It has several nice features including the ability to set alarms to remind you of appointments. I use one of the older versions (0.7) which ports well to newer versions of FLTK and, per my recommendation, so does NanoLinux.

Simple todo list. Haven't used it in a while, but if you're looking for a todo list program, it's an option.

PDF/Ebook Readers

A functional, basic PDF viewer and archived image viewer. I really like this one. It requires a compiler with later C++ support to build. Needs minimal dependencies, mainly libarchive and poppler. While poppler isn't as fast as mupdf at rendering, this still works pretty fast.

Image viewer with plugin support for mupdf and poppler.

There's also flaxpdf which is optimized for efficiency and uses mupdf. However, it's not at all portable to non-POSIX systems.

I tried BDReader as well but there are a lot of dependencies involved in building this.

File managers

I don't use any of these and personally prefer the SDL based file manager mentioned earlier. However, they're nice lightweight GUI file managers. I'm sure there are a few others not mentioned below as well.



Other POSIX only FLTK applications

GUI front end for synaptics touchpad controls.

FLTK ALSA Mixer front end.


I've yet to find a FLTK based editor I really like. For now, I'm still using SciTE, Fxite and nano.

I would love to find a Scintilla based FLTK editor. The closest I've found is

There are many FLTK editor controls out there, including the one used by Postoffice.

Nanolinux offers flwriter.

The most interesting editor option I've found so far is fldev. There's a link to the original at and further development by the developer of NanoLinux at The main drawback is that it only opens one file at a time. The original author began to add support to use it as a debugger in conjunction with gdb. I'd love to get that support working properly and in a cross-platform manner and have been experimenting with it as time allows.

flabc is an editor specifically designed for ABC notation, but it appears to be a stable, well-written editor and may be useful for other editing purposes.
Here's a list of music/audio software I like or have found of interest. I've built all of them from source without too many complications at one point or another. I'm also working on patching apcstudio which is a lightweight FLTK based audio/wave file editor. I have it building with the latest version of FLTK and am hoping to add some new capabilities.

URLs are accurate as of when this was posted. However, they can change over time. You can use a search engine or wayback tool to find pages that have been moved or backups of older versions of pages.

Multi-track audio editor and recorder. It can be used to record real instruments and create sound samples.

Create and listen to mod and xm files. Sound quality for playing mod files is better than many other mod file players.

Midi player. Can convert midi to wave files. Some versions show piano keyboard(s) with notes as they play. Can show lyrics of Karaoke midi files.

Convert ABC notation (which can be created in any text editor) to midi and back again.

Convert ABC notation to Postscript sheet music for printing. One can even add guitar tablature using special fonts.

sox - SOund eXchange
Swiss army knife of sound processing programs. Audio conversion utilities.

Records/plays audio and has audio filtering to remove noise.

FLTK Midi Keyboard
On screen Midi Keyboard using FLTK GUI library and rtmidi MIDI library.

SDL Widgets examples
Various audio programs including BigBand for music composition, SDL Widgets examples to make and edit waveforms and a synthesizer for Android devices.

Paul's Extreme Sound Stretch. Stretches audio files. FLTK GUI.

GUS patch tools
Gus patch utilities based on timidity-tools.

Midi utilities with GUS support

July 2017

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