Identi.ca is based on the StatusNet software (formerly called Laconi.ca), which is freely available for download and install, and may be used by other websites for creating their own microblogging services.
Users post short (up to 140 characters) notices which are broadcasted to their friends and fans using the Web, RSS, mobile phones, instant messages or different other means.
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 OStatus protocol, meaning that you can have friends on other microblogging services that can receive your notices and reply back to your service.
The goal here is autonomy — you deserve the right to manage your own online presence. If you don't like how Identi.ca works, you can take your data and the source code and set up your own service (or move your account to another one).
 See also
- Wikipedia's article on Identi.ca
- Recent Identi.ca bookmarks on Delicious
- Some of the news stories about Identi.ca: