A non-proprietary, patent free open source audio compression format that is similar to MP3.
Ogg Vorbis is a completely open, patent-free, professional audio encoding and streaming technology with all the benefits of Open Source.
Related: Icecast, Zinf, Jargonfile - Ogg
Also see Theora, Free Video Compression from Xiph
Ogg, Flac and Mod file support for Adobe Audition (& CoolEdit)