http://www.xiph.org/ogg/vorbis/
It is a mp3 like encoding / decoding CODEC. Still real early, but seemingly with promise and a dedication to release. It claims to be patent free and open, although the company (xiph) is keeping the codec itself under their control.
I've heard of it but haven't looked at it very closely yet. A lot of the documentation for the spec is still missing, although a look at the code may be revealing.
Is there growing momentum for it?
I just joined their mailing list.
-rob