StatusNet, the open source micro blogging ("Twitter-like", with a stress on like) platform has gone though a ton of changes since it's launch in 2008. I started playing around with the idea in mid 2008 and eventually got my Statusnet (formerly known as Laconica) running in December 2008. The project is under very active development and was hosted as a community called Identi.ca. Developer Evan Prodromou, and now CEO of Statusnet created some standards to allow instances of statusnet to talk to one another and subscribe to remote users without having to belong to every community.
The open nature of remote subscription breaks down the "walled garden" of having to belong to every community (i.e. Facebook and Twitter) and communicate openly across the various community lines. StatusNet has introduced many new technologies that all you to participate anyway you like, whether it is via IM, SMS, Twitter, FaceBook to name a few. Here is the list of features that is accessible from the help.
I recently upgraded to the most currently build 0.9.3 which added a number of fixes and additional features, one of which is the new StatusNet desktop. It is limited compared to other clients out there but it is build on open technologies and does not use Adobe Air (YES!). The feature set is growning and the more communities there are, the more stable it will be! ~Lou