Icecast is a streaming media (audio/video) server which currently supports Ogg (Vorbis and Theora), Opus, WebM and MP3 streams.
It can be used to create an Internet radio station or a privately running jukebox and many things in between. It is very versatile in that new formats can be added relatively easily and supports open standards for communication and interaction.
Icecast is distributed under the GNU GPL, version 2.
Icecast is an open source project of xiph.org, the people who brought us Ogg Vorbis.
I am using Icecast for MixRemix Radio. Right now I am using Caster.fm but I am in the process of moving to my own server. Caster.fm has a free service that I recommend if you want to run your own Icecast Radio without having to invest. I also recommend Anonradio, a supportive community of DJs using Icecast hosted on SDF servers.