Mastodon is an alternative implementation of GNU social, a free,
open-source social network.  It is a decentralized alternative to
commercial platforms based on ActivityStreams, Webfinger, PubsubHubbub
and Salmon.  The project focuses on creating a clean REST API and a good
user interface.  Ruby on Rails is used for the back-end, while React.js
and Redux are used for the dynamic front-end.