Pleroma : Pleroma is a federated social networking platform, compatible with GNU social and other OStatus implementations. It is free software licensed under th...
pump.io : Social server with an ActivityStreams API. It's a stream server that does most of what people really want from a social network.
gollum : A simple, Git-powered wiki with a sweet API and local frontend.
Fireworq : Fireworq is a lightweight, high-performance, language-independent job queue system.
Gibber : Gibber is a live coding environment for the web browser, using the Gibberish.js audio engine, the CodeMirror code editor library and wrapping Three.js...
GNU social is a continuation of the StatusNet project. It is social communication software for both public and private communications. It is widely supported and has a large userbase. It is already used by the Free Software Foundation.