Speex is an audio codec that joined Xiphophorus (xiph.org) development force in October 2002. It is intended to become a sister format for Ogg Vorbis. Speex is in beta testing.
Like many other things, Speex is wrapped inside Ogg bitstream container. Unlike Vorbis, Speex is intended for use with very low bitrates (6 - 32 kbps), and as name suggests, it's best for compressing speech. In addition to the usual 16-bit sample format, it also supports 8-bit data. It works in VBR, and also supports voice activity detection (no speech means less data)...
Like Vorbis, speex is unencumbered by software patents. The code is distributed under the terms of Xiph's BSD variant license.
Speex is intended to be used in speech transmission in applications like VoIP and internet telephony, and also to store speech data locally (voice mail archiving and audio books are listed as examples).
Some applications that use Speex include LinPhone, OpenH323 and GnomeMeeting.
Home page: http://www.speex.org/ (where most of this stuff was taken from)