|This is a video codec. The name to use at the command line is theo.|
This codec can be used inside the ogg and matroska containers.
It's being developed by the Xiph.org Foundation of Ogg and Vorbis fame. If you want to be sure there are no legal issues with your software, Theora is a good choice, although it's technically not as advanced as MPEG-4 or WMV9.
Version 1.0 of the codec has been released in 2008 November, in 2009 September version 1.1 came out, improving the encoding quality while preserving full compatibility. The video format is frozen (has been since 2004, but there are buggy videos produced by old encoders around and not playing well) so it's safe to produce Theora files for future use.
Theora files can be streamed using the Icecast 2 streaming server, available for most recent Linux distributions.