Some other decentralized/federated applications:
diaspora* (Social Network) - https://diasporafoundation.org/
MediaGoblin (Media Sharing) - http://mediagoblin.org/
pump.io (Social Network)- used by https://identi.ca/ and others
GNU Social - https://gnu.io/
Hubzilla - https://hubzilla.org
Friendica - http://friendica.com/
Tent (Protocol) - https://tent.io/ - not sure if this is active any more
Activity Streams (W3C Standard) - https://www.w3.org/TR/activitystreams-core/
Lots of great interviews on decentralized technologies here: http://redecentralize.org/interviews/
Comments like this are what makes viewing the comments part worth its time.
I did not upvote it because I know that once 7 days had passed, upvoting does no good and in fact does bad by wasting voting power.