StatusNet (formerly Laconica) is a microblogging service. Users post short (140 character) notices which are broadcast to their friends and fans using the Web, RSS, or instant messages. It is the software that runs Identi.ca.
OpenMicroBlogger is the 2nd implementation of the http://openmicroblogging.org standard for distributed microblogging. Install it and subscribe/post notices via http://identi.ca or http://army.twit.tv and many other sites.
Rizzoma is an online collaboration tool for small projects, ideal for teams of 5 to 25 people, providing a natural way of communication. The main advantage of this tool is an immediate generation of documents based on a discussion thread.