lmemsm

Below is a list of code that is in the public domain or available under CC0 or unlicense or 0BSD terms.

The MinGW win32 API headers and mingw runtime library were originally released to the public domain. Although the mingw.org project prefers to differentiate itself from mingw64, the developers have followed the mingw64 project's example and licensed later versions of the w32api and mingwrt. I contacted the mingw.org project to ask if they would consider dual licensing using their current license and CC0, but they refused. It was at that point that I left the MinGW project. Needing to distribute license information with every program I build with my C/C++ compilers did not seem like a worthwhile trade-off. The last public domain version of w32api is w32api-3.17-2-mingw32-src.tar.lzma. The last version of mingwrt with some public domain code is mingwrt-3.20-2-mingw32-src.tar.lzma.

I am currently maintaining a version of w32api based on the last public domain version available. I have added some patches that never made it in to either mingw or mingw64. While it's not fully up-to-date with all the changes in the latest versions of Windows, it does support enough compatibility to be able to build several Open Source libraries on Windows. I also intend to keep backward compatibility with older versions of Windows for as long as can. I hope to replace the mingwrt library with something far more portable that includes support for some POSIX and C11 features. I already have bits and pieces coded from scratch including C11 and POSIX threading libraries. One of the purposes of this list is to find public domain source that might be useful to add to a C runtime library.

If you have recommendations for public domain/Unlicense/CC0 C/C++ functions, libraries and programs that I have missed, please let me know. Also feel free to contact me about my work maintaining the public domain version of w32api or my project to replace the mingwrt. You can contact me via the CppDesign mailing list or e-mail me: http://www.distasis.com/connect.htm

Public domain C runtime libraries:
PDCLib
http://pdclib.e43.eu/
Original Public Domain C library
https://sourceforge.net/projects/pdclib/
https://sourceforge.net/projects/pdos/
Another fork of PDCLib
https://github.com/DevSolar/pdclib
libc11
https://github.com/dryc/libc11
Eltanin-OS simia
https://github.com/eltanin-os/simia

dlmalloc - Doug Lea's memory allocator
http://gee.cs.oswego.edu/

SQLite database - includes sprintf code
https://www.sqlite.org/index.html

LibTom projects - cryptography and math libraries
https://github.com/libtom

strftime
https://github.com/arnoldrobbins/strftime

tz
https://github.com/eggert/tz

whereami
https://github.com/gpakosz/whereami

minlib - regexp and other small libraries
https://github.com/ccxvii/minilibs

tiny-regex-c
https://github.com/kokke/tiny-regex-c

tiny-regex
https://github.com/matp/tiny-regex

getline
https://github.com/ChristopherWilks/megadepth/blob/master/getline.c

getline
https://github.com/arnavyc/getdelim

getline
https://github.com/digilus/getline

getline
https://github.com/ivanrad/getline

getopt
https://github.com/skeeto/getopt

parg
https://github.com/jibsen/parg

sdbm (ndbm clone), basic regex, glob, also links to prolog and yacc
http://www.cse.yorku.ca/~oz/

Base64 encode/decode:

base64
https://www.fourmilab.ch/webtools/base64/

Race64
https://github.com/skeeto/race64

Compression:

miniz - zlib compression
https://code.google.com/archive/p/miniz/

zip - portable zip library based on miniz
https://github.com/kuba--/zip

liblzw - Compression/decompression library for LZW files with API comparable to zlib and libbzip2. LZW is used by UNIX compress/decompress programs which work with files with a .Z extension. I use this library with BSD gzip.
https://github.com/vapier/liblzw

ncompress - LZW compression/decompression tools
https://github.com/vapier/ncompress

unzoo - zoo unarchiver
http://freshmeat.sourceforge.net/projects/unzoo/

stdarc - compressors/decompressors collection
https://github.com/r-lyeh/stdarc.c

mousetar
https://pkgs.org/download/mousetar

dxTarRead - non-compressing archive file reader
https://github.com/DeXP/dxTarRead

Cryptography:

NaCl - crypto library
https://nacl.cr.yp.to/

TweetNaCl - crypto library
http://tweetnacl.cr.yp.to/software.html

Monocypher - crypto library
https://monocypher.org/

Kripto
https://github.com/rofl0r/kripto

WjCryptLib
https://github.com/WaterJuice/WjCryptLib

Crypto++ - Individual files are public domain
https://www.cryptopp.com/

tiny-AES-c
https://github.com/kokke/tiny-AES-c

retter
https://github.com/MaciejCzyzewski/retter

blasha1
https://github.com/FRex/blasha1

Random Number Generators:

pseudo random number generator and other files
https://github.com/Marc-B-Reynolds/Stand-alone-junk/tree/master/src/SFH
http://marc-b-reynolds.github.io/shf/2016/04/19/prns.html

UTF-8:

utf8 string functions
https://github.com/sheredom/utf8.h

Console:

pd_readline
https://github.com/mooseman/pd_readline

INI reader
https://github.com/seb-jones/simple-ini-reader

terminfo parser
https://github.com/agauniyal/termdb

library for drawing colors on terminals
https://github.com/agauniyal/rang

snore
https://github.com/FRex/snore

GUIs:

Nuklear - immediate mode GUI
https://github.com/Immediate-Mode-UI/Nuklear
https://github.com/vurtun/nuklear

D-Flat - graphics libbrary published in Dr. Dobb's Journal
https://github.com/mooseman/D-Flat

Turbo Vision
http://tvision.sourceforge.net/

wtk - cross-platform immediate mode GUI library
https://github.com/origamicomet/wtk

Vogle - graphics library
https://github.com/mooseman/Vogle

Math libraries:

FGMP - public domain implementation of a subset of the GNU gmp library with the same API
https://github.com/dad98253/fgmp

C++ Big Integer Library
https://mattmccutchen.net/bigint/

tiny-bignum-c
https://github.com/kokke/tiny-bignum-c

triglib
https://github.com/richgel999/triglib

meow_fft
https://github.com/JodiTheTigger/meow_fft

FFT library
https://github.com/wareya/fft

Communications:

irc library
https://github.com/domsson/libtwirc

irc client
https://git.janouch.name/p/uirc3/

nanoircd IRC server
https://github.com/joric/nanoircd

youtube-dl
http://ytdl-org.github.io/youtube-dl/about.html

streams federated communications server
https://codeberg.org/streams/streams

Programs and utilities:

pdksh
https://directory.fsf.org/wiki/Pdksh

es - extensible shell
http://wryun.github.io/es-shell/

byacc - Berkeley Yacc
https://invisible-island.net/byacc/byacc.html

miniAWK
https://github.com/mooseman/miniAWK

pdcore - public domain core utilities
https://github.com/mooseman/pdcore

pdutils - public domain utilities
https://github.com/mooseman/pdutils

unidiff - unified diff conversion
https://github.com/AceHusky12/unidiff

make
https://github.com/mumu3w/MINIX1x_OLD/tree/master/minix1.3_tc2_tasm/commands/make

touch utility
http://roy.orz.hm/svn/filedetails.php?repname=rtoss&path=%2Ftouch%2Ftouch.c

md5sum utility plus other CC0 utilities at the site:
http://myc01.free.fr/md5sum/

ripgrep - recursively searches directories for a regex pattern
https://github.com/BurntSushi/ripgrep/

pstree
https://github.com/janmojzis/pstree

xd - hex dump tool
https://www.ttgurney.com/xd.c

sc - spreadsheet calculator
http://www.ibiblio.org/pub/Linux/apps/financial/spreadsheet/!INDEX.html

scientific calculator
https://github.com/MostafaMahmoudAbdelrahman/scientific-calculator

cron and crontab
https://github.com/somnisoft/cron

tinyssh - ssh server
https://github.com/janmojzis/tinyssh

curvevpn
https://github.com/janmojzis/curvevpn

smtp-client
https://github.com/somnisoft/smtp-client

POP3 + SMTP server
https://github.com/skeeto/minimail

Epoch - Linux init system
https://universe2.us/epoch.html

sunrise and sunset
https://github.com/troglobit/sun

perpetual calendar
https://github.com/randruc/PerpetualCalendar

Virtual Machine
https://github.com/wasmite/wasabi

Hedley - compiler compatibility project
https://nemequ.github.io/hedley/

subc - compiler for a subset of the C language
http://www.t3x.org/subc/

BDS C - 8080/Z80 C Compiler
https://www.bdsoft.com/resources/bdsc.html

microprofile - profiler
https://github.com/jonasmr/microprofile

mpkg - package manager
http://charon.persephoneslair.org/~andrea/software/mpkg/

Games:

nbsdgames
https://github.com/untakenstupidnick/nbsdgames

Connect Four
https://github.com/skeeto/connect4

tile-solver
https://github.com/skeeto/tile-solver

flappy bird
https://github.com/skeeto/flappy

anarch
https://gitlab.com/drummyfish/anarch

kiki
https://sourceforge.net/projects/kiki/

Diamond Trust
http://hcsoftware.hg.sourceforge.net/hgweb/hcsoftware/DiamondTrust/

Behacked - bejeweled clone
https://github.com/Pentachoron-Labs/Behacked

Personal assistant:

Oracle - siri/alexa/google-assistant like chatbot
https://github.com/TheShoutingParrot/Oracle

Various projects
https://github.com/mooseman
https://github.com/mooseman/mooseman_stuff

Small and single file libraries:

image, sound, sprintf, Truetype font and other code
https://github.com/nothings/stb

public domain single file libraries
https://github.com/mackron/dr_libs

cute headers
https://github.com/RandyGaul/cute_headers

foundation library
https://github.com/mjansson/foundation_lib

single file public domain libraries
https://github.com/gingerBill/gb

single file public domain libraries
https://github.com/haunticaachris/htc

single file public domain libraries
https://github.com/mattiasgustavsson/libs

single file libraries in the public domain
https://github.com/to-miz/tm

stb inspired libraries
https://github.com/AfroDave/kj

single header libraries
https://github.com/Cyphre117/header-libraries

single header library for CLI
https://github.com/ronen25/libcmdf

tiny bits and useful snippets
https://github.com/r-lyeh/tinybits

public domain single file libraries
https://github.com/kieselsteini/sts

CLM_LIBS - useful code and macros
https://github.com/CarlosLunaMota/CLM_LIBS

vlib - single file header libraries for C
https://github.com/vktec/vlib

ZPL - your (almost) C99 Powerkit
https://github.com/zpl-c/zpl

FYS
https://github.com/germinolegrand/fys

portable public domain code snippets
https://github.com/nemequ/portable-snippets

code snippets and header-only files
https://github.com/DanielGibson/Snippets/

json parser
https://github.com/sheredom/json.h

Database:

tinycdb
http://www.corpit.ru/mjt/tinycdb.html

Lexical analysis:

re2c
https://re2c.org/

Data structures:

avl tree
https://github.com/etherealvisage/avl

avl tree
https://github.com/ebiggers/avl_tree

nbds - Non-blocking data structures
https://code.google.com/archive/p/nbds/

sack
https://github.com/FRex/sack

Editor:

kakoune - code editor
https://github.com/mawww/kakoune

Audio:

libmodplug
https://github.com/Konstanty/libmodplug

miniaudio
https://github.com/dr-soft/miniaudio

tonic
https://github.com/TonicAudio/Tonic

mp3_id3_tags
https://github.com/Arcxm/mp3_id3_tags

rsynth - text-to-speech system
http://www.speech.cs.cmu.edu/comp.speech/Section5/Synth/rsynth.html

voclib - vocoder
https://github.com/blastbay/voclib

Graphics:

gif-h
https://github.com/charlietangora/gif-h

gifdec
https://github.com/lecram/gifdec

gifenc
https://github.com/lecram/gifenc

gif-load
https://github.com/hidefromkgb/gif_load

GIF Writer
https://www.jonolick.com/home/gif-writer

jpeg-compressor
https://github.com/richgel999/jpeg-compressor

TinyJPEG
https://github.com/serge-rgb/TinyJPEG/

picojpeg
https://github.com/richgel999/picojpeg

analyzepng
https://github.com/FRex/analyzepng

topng
https://github.com/FRex/topng

binarypic
https://github.com/FRex/binarypic

libplum
https://github.com/aaaaaa123456789/libplum

miniexr
https://github.com/aras-p/miniexr

MPEG video writer
https://www.jonolick.com/home/mpeg-video-writer

gameswf
http://tulrich.com/textweb.pl?path=geekstuff/gameswf.txt

PDFGen
https://github.com/AndreRenaud/PDFGen

libqrgen
https://github.com/aaaaaa123456789/libqrgen

public domain single file libraries for games
https://github.com/pennie-quinn/paq

Game engines:

AVA - game engine
https://github.com/r-lyeh/AVA

L - game engine
https://github.com/Lyatus/L

Phyxed 2D - 2D physics engine with fixed point math
https://github.com/Srekel/phyxed-2d

easytab - tablet library
https://github.com/ApoorvaJ/EasyTab

Graphics and math:

HandmadeMath - math library for games and graphics
https://github.com/HandmadeMath/Handmade-Math

small3dlib - fast, small, efficient, portable, public domain 3D software rasterizer
https://gitlab.com/drummyfish/small3dlib

raycastlib - fast, small, efficient, portable, public domain ray casting library
https://gitlab.com/drummyfish/raycastlib

pt_math - scalar math
https://github.com/pmttavara/pt_math

linmath.h - lean linear math library for graphics
https://github.com/datenwolf/linmath.h

single file C/C++ libraries - raytracer, etc.
https://github.com/rmitton/rjm

graphics code
http://fileadmin.cs.lth.se/cs/Personal/Tomas_Akenine-Moller/code/

Immediate2D Drawing Framework
https://github.com/npiegdon/immediate2d

TIGR - Tiny Graphics Library
https://github.com/xahon/tigr

Debug Draw - immediate mode drawing API
https://github.com/glampert/debug-draw

lightmapper
https://github.com/ands/lightmapper#lightmapper

seamoptimizer
https://github.com/ands/seamoptimizer

tinygizmo
https://github.com/ddiakopoulos/tinygizmo

image resampler
https://github.com/richgel999/imageresampler

vector and matrix library
https://github.com/jobtalle/ccVector

vector math library
https://github.com/sgorsten/linalg

sts - vertex cache optimization
https://github.com/Sigkill79/sts

cro lib - mipmap generator
https://github.com/thebeast33/cro_lib

GUI apps for OSX in C
https://github.com/hidefromkgb/mac_load

Lightweight TUI display manager for Linux and BSD
https://gitlab.com/TilCreator/ly

OS:

TempleOS is an original operating system written in a variant of C called HolyC
https://github.com/cia-foundation/TempleOS

Tforth is a very tiny toy OS written for the IBM PC in 8086 assembly language inspired by the FORTH programming language
https://www.ttgurney.com/tforth.asm