GNU social

GNU social (previously known as StatusNet and once known as Laconica) is a free and open source software microblogging server written in PHP that implements the OStatus standard for interoperation between installations. While offering functionality similar to Twitter, GNU social seeks to provide the potential for open, inter-service, and distributed communications between microblogging communities. Enterprises and individuals can install and control their own services and data.
GNU social has been deployed on hundreds of interoperating servers.
History.
GNU social was spun out of the GNU FM project. The founder was Matt Lee and the early developers were fellow FSF employees, Donald Robertson and Deborah Nicholson.
StatusNet deployment based on the formerly known as Laconica was the Identi.ca open-microblogging service. Hosted by original StatusNet creators StatusNet Inc., Identi.ca offered free accounts to the public and serves as the co-flagship (along with freelish.us) for the installable version of StatusNet. The site has migrated to pump.io.
Version 0.9.0, released March 3, 2010, added support for OStatus, a new distributed update standard superseding OpenMicroBlogging.
June 8, 2013 it was announced StatusNet would be merged into the GNU social project, along with Free Social.
The service is interoperable with other OStatus platforms.
Names.
StatusNet was renamed from Laconica coinciding with the release of version 0.8.1 (a.k.a. "Second Guessing") of the StatusNet software.
StatusNet's name "simply reflects what our software does: send "status" updates into your social "net"work."
Laconica's name was a reference to the Laconic phrase, a particularly concise or terse statement the likes of which are famously attributed to the leaders of Sparta (Laconia being the Greek region containing Sparta). In microblogging, all messages are forced to be very short due to the ~140 character tradition on message size, thus they are all de facto laconic phrases.
The GNU in the name refers to the GNU Project.