Akkoma - Federated microblogging server with Mastodon, GNU social, and ActivityPub compatibility. (Source Code) AGPL-3.0Elixir/Docker
Answer - Knowledge-based community software. You can use it to quickly build your Q&A community for product technical support, customer support, user communication, and more. (Source Code) Apache-2.0Docker/Go
Artalk - Comment system built in Golang, providing a lightweight and highly customizable solution for adding comments to your website. (Source Code) MITGo/Docker
AsmBB - Fast, SQLite-powered forum engine written in ASM. (Source Code) EUPL-1.2Assembly
BuddyPress - Powerful plugin that takes your WordPress.org powered site beyond the blog with social-network features like user profiles, activity streams, user groups, and more. (Source Code) GPL-2.0PHP
Discourse - Advanced forum / community solution based on Ruby and JS. (Demo, Source Code) GPL-2.0Docker
Elgg - Powerful open source social networking engine. (Source Code) GPL-2.0PHP
Enigma 1/2 BBS - Enigma 1/2 is a modern, multi-platform BBS engine with unlimited "callers" and legacy DOS door game support. (Source Code) BSD-2-ClauseShell/Docker/Nodejs
Flarum - Delightfully simple forums. Flarum is the next-generation forum software that makes online discussion fun again. (Source Code) MITPHP
Misago - Fully featured modern forum application that is fast, scalable and responsive. (Source Code) GPL-2.0Docker
Misskey - Decentralized app-like microblogging server/SNS for the Fediverse, using the ActivityPub protocol like GNU social and Mastodon. (Source Code) AGPL-3.0Nodejs/Docker
Movim - Modern, federated social network based on XMPP, with a fully featured group-chat, subscriptions and microblogging. (Source Code) AGPL-3.0PHP/Docker
MyBB - Free, extensible forum software package. (Source Code) LGPL-3.0PHP
NodeBB - Forum software built for the modern web. (Demo, Source Code) GPL-3.0Nodejs/Docker
OSSN - Social networking software that allows you to make a social networking website and helps your members build social relationships, with people who share similar professional or personal interests. (Source Code) CAL-1.0PHP
phpBB - Flat-forum bulletin board software solution that can be used to stay in touch with a group of people or can power your entire website. (Source Code) GPL-2.0PHP
PixelFed - Ethical photo sharing platform, powered by ActivityPub federation (alternative to Instagram). (Source Code) AGPL-3.0PHP
qpixel - Q&A-based community knowledge-sharing software. (Source Code) AGPL-3.0Ruby
Redlib⚠ - An alternative private front-end to Reddit, with its origins in Libreddit. AGPL-3.0Rust
remark42 - A lightweight and simple comment engine, which doesn't spy on users. It can be embedded into blogs, articles or any other place where readers add comments. (Demo, Source Code) MITDocker/Go
Retrospring - A free, open-source social network following the Q/A (question and answer) principle of sites like Formspring, ask.fm or CuriousCat. (Demo) AGPL-3.0Ruby/Nodejs
Scoold - Stack Overflow in a JAR. An enterprise-ready Q&A platform with full-text search, SAML, LDAP integration and social login support. (Demo, Source Code) Apache-2.0Java/Docker/K8S
Simple Machines Forum - Free, professional grade software package that allows you to set up your own online community within minutes. (Source Code) BSD-3-ClausePHP
Socialhome - Federated and decentralized profile builder and social network engine. (Demo, Source Code) AGPL-3.0Docker/Python
Talkyard - Create a community, where your users can suggest ideas and get questions answered. And have friendly open-ended discussions and chat (Slack/StackOverflow/Discourse/Reddit/Disqus hybrid). (Demo, Source Code) AGPL-3.0Docker/Scala
yarn.social - Self-Hosted, Twitter™-like Decentralised micro-logging platform. No ads, no tracking, your content, your data. (Source Code) MITGo
Zusam - Free and open-source way to self-host private forums for groups of friends or family. (Demo) AGPL-3.0PHP