Misskey

Federated microblogging server.

Advanced forum / community solution based on Ruby and JS.

Delightfully simple forums. Flarum is the next-generation forum software that makes online discussion fun again.

Forum software built for the modern web.

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.

Link aggregator for the fediverse (alternative to Reddit).

Distributed social networking server.

An alternative front end to twitter.

Pixelfed is an open-source, federated platform alternate to Instagram.

Flexible kit for private social networks.

Lightweight commenting server written in Python and Javascript. It aims to be a drop-in replacement for Disqus.