Learning Management Systems, Course Management Systems, Virtual Learning Enviornments, Student Information Systems and other FLOSS online tools that may be useful for Education:

https://jitsi.org/
Recently tried Jitsi and found it very easy to use for online conferences and meetings. If you don't have a browser that works with the software, there's a mobile app option. Want to set up a meeting for your group or class with video and audio support? Check it out. Hosts approx. 75 concurrent users.

https://bigbluebutton.org/
https://bigbluebutton.org/integrations/
BigBlueButton is a web conferencing system that can integrate with various LMS programs. Hosts at least 200 concurrent users.

https://www.mumble.info
https://f-droid.org/packages/se.lublin.mumla/
Mumble is a free, Open Source, low latency, high quality voice chat application. Mumla is an Android app for the Mumble voice conference system. Mumble can handle 1000 concurrent users.

http://llcon.sourceforge.net/
Jamulus software enables musicians to perform real-time jam sessions over the internet. Latest version can handle around 100 concurrent users playing together. Hosts at least 50 concurrent users.

https://sonobus.net/
Sonobus is an easy to use application for streaming high-quality, low-latency peer-to-peer audio between devices over the internet or a local network. 12 concurrent users maximum.

https://obsproject.com/
Open Broadcaster Software for video recording and live streaming.

https://joinpeertube.org/en_US
Share videos online.

https://mediagoblin.org/
Decentralized media publishing platform.

https://owncast.online/
Live video and web chat.

https://gettogether.community/about/
Open Source event manager for local communities. Share your own events and meetings at the site or try the software to host your own event manager.

https://joinmobilizon.org/en/
Mobilizing tool to organize gatherings.

https://gancio.org/
Shared agenda for local communities.

https://gath.io/
Event sharing platform.

https://appinventor.mit.edu/
Make your own mobile apps to share with others.

https://camstudio.org/
Windows users who want to record their desktop can use CamStudio and share the results online.

https://moodle.org/
Moodle is a learning platform, LMS and course management system (CMS).

https://atutor.github.io/
ATutor is an Open Source LMS, used to develop and manage online courses, and to create and distribute interoperable elearning content.

https://github.com/instructure/canvas-lms/wiki
Canvas is a modern, Open Source LMS released under the AGPLv3 license.

https://sourceforge.net/projects/ilias/
ILIAS is a web base learning management system (LMS, VLE, CMS)

https://github.com/claroline/Claroline
https://claroline.net/
Claroline is a collaborative eLearning and eWorking platform (learning management system) released under the GPL open-source license

https://olat.org/
OLAT is a Learning Management System that supports any kind of online learning, teaching, and tutoring with few educational restrictions

https://chamilo.org/en/
Chamilo is e-learning and collaboration software

https://www.dokeos.com/
Dokeos is a LMS, CMS and e-learning suite

https://github.com/pupilfirst/pupilfirst
Pupilfirst is a LMS

https://www.sakailms.org/
Sakai is a free, community source, educational software platform designed to support teaching, research and collaboration, LMS and CMS

https://www.xerte.org.uk/index.php/en/
E-learning development environment.

https://gibbonedu.org/
Gibbon is a flexible, open source school management platform

https://safeexambrowser.org/news_en.html
SEB, the Safe Exam Browser, can be used in conjunction with
various LMS software.

https://elgg.org/
Elgg is an award-winning Open Source social networking engine that provides a robust framework on which to build all kinds of social environments, from a campus wide social network for your university, school or college or an internal collaborative platform for your organization

https://tcexam.org/
TCExam is a Open Source system for electronic exams (also know as CBA - Computer-Based Assessment, CBT - Computer-Based Testing or e-exam) that enables educators and trainers to author, schedule, deliver and report on quizzes, tests and exams

https://github.com/jkitchin/techela-emacs
Techela, Technology enhanced learning and assessment, is a framework for teaching courses and provides a way to distribute, collect, grade, and return digital assignments

https://projectfedena.org/
Project Fedena is a Free and Open Source school management application that has more features than a student information system

https://www.edutracsis.com/
https://sourceforge.net/projects/edutrac/
eduTrac SIS is a Free and Open Source student information system for higher education that allows educational institutions to manage faculty, staff, students, courses, course registrations and more

https://www.rosariosis.org/
RosarioSIS is a Free and Open Source Student Information System (SIS), School Management System (SMS) and School ERP

https://opensis.com/
OpenSIS is the best user friendly open source student information system plus full scale school management and administrative system

https://en.wikipedia.org/wiki/SchoolTool
SchoolTool is a GPL licensed, free student information system for schools around the world

https://sourceforge.net/projects/fet-timetabling/
FET is free timetable software for schools

http://richtech.ca/
Open Admin for Schools is a school administration program

https://github.com/inverse-inc/sogo
Groupware for calendar, e-mail and address book access.

https://github.com/veyon/veyon
Veyon (Virtual Eye On Networks, formerly iTALC) is free and open source software for computer monitoring and classroom management supporting Linux and Windows

https://www.sparkleshare.org/
SparkleShare is an Open Source cloud storage and file synchronization client app

https://github.com/Sankore/Sankore-3.1
Open-Sankore is an Open Source interactive whiteboard

https://openmeetings.apache.org/
OpenMeetings is software used for presenting, online training, web conferencing, collaborative whiteboard drawing and document editing and user desktop sharing.

https://gobby.github.io/
Gobby is a collaborative editor supporting multiple documents in one session and a multi-user chat

https://www.libreoffice.org/download/libreoffice-online/
LibreOffice Online provides collaborative editing through a web browser.

https://secure.plaimi.net/games/quizbot.html
Simple quizbot for IRC.

https://wordpress.com/blog/2020/08/06/improve-your-remote-collaboration-with-p2/
P2 is currently Software As A Service, but a self-host Open Source version is in the works.

https://code.google.com/archive/p/gpapers/
gPapers is an Open Source digital library manager. Think of it as an iTunes for your PDFs.