AudioGalaxy

AudioGalaxy was a file-sharing system that indexed MP3 files. Founded by Michael Merhej and sporting a web-based search engine, always-on searching for requested files, auto-resume and low system impact.
Although AudioGalaxy's primary purpose was clearly to facilitate sharing of music, much more has grew out of it. AudioGalaxy was notable for its strong community due to such features as chat-enabled groups and per-artist message boards.

AudioGalaxy's client only supported Windows (32 bits) platforms and it's protocol was closed.

AudioGalaxy was sued by a recording industry and had to stop it's service.

This text has been taken from Wikipedia (here) under the GNU FDL public license.

NOTE: aMule is a separate project and is not related to AudioGalaxy in any way. More over, aMule does not support AudioGalaxy's protocol.