Cygnal is a Flash media server compatible audio and video server. Since this is a new sub project of Gnash, it's currently only a prototype, and not yet available. This info is about what it will be.
It will need to handle many thousands of simultaneous network connection, and support running on large GNU/Linux clusters. It should support handling multiple streams with differing content, as well as a multicast stream with a single data source.
There are several other streaming servers that handle streaming audio and video. Some handle multiple formats, but most have a protocol supported only by that one project. (like shoutcast) None but Red5 support Flash, and that feature isn't working yet anyway.
Due to the patent issues surrounding MP3, and the fact that FLV and ON2 are closed formats, one of the main goals of this project is to support free codes and free protocols as the primary way of doing things. Optionally there will be support for MP3, FLV, and ON2 (VP6 and VP7) when playing existing Flash content. Both FLV and the VP6 & VP7 codecs are included in ffmpeg. Users can use the ffmpeg plugin for Gstreamer to use these proprietary codecs.
For more information, go to the Cygnal Page on the developers wiki.