Ogg Vorbis is an open source digital audio technology designed to compete with MP3. Unlike MP3, Ogg Vorbis has no patents and can be used and developed by anyone. Ogg Vorbis is part of the open source Ogg project that aims at creating a completely free and open multimedia system. Ogg Vorbis files end with the extension .ogg and require supported players for listening.
Ogg Vorbis developers claim they use a superior psychoacoustic model that yields better sounding files than MP3 at comparable bitrates. I suggest a listening test yourself to compare an MP3 and Ogg Vorbis file encoded at the same bitrate.