Identi.ca, Open MicroBlogging platform
an Open Source, CreativeCommons framework for a distributed network of federated microblogging services.
"How is Identi.ca different from Twitter, Jaiku, Pownce, Plurk, others?
Identi.ca is an Open Network Service. Our main goal is to provide a fair and transparent service that preserves users' autonomy. In particular, all the software used for Identi.ca is Free Software, and all the data is available under the Creative Commons Attribution 3.0 license, making it Open Data.
The software also implements the OpenMicroBlogging protocol, meaning that you can have friends on other microblogging services that can receive your notices
The goal here is autonomy -- you deserve the right to manage your own on-line presence. If you don't like how Identi.ca works, you can take your data and the source code and set up your own server (or move your account to another one)." (http://identi.ca/doc/faq)