Tracker modules are a versatile format used by many older games as well as portable systems such as Nintendo GameBoy Advance. If Second Life supported them, it would remove the need for the 10 second limit currently imposed on scripts, and parcel music could be hosted directly without requiring people to use an external ShoutCast server.
This is possible because tracker modules have the following advantages over MP3/OGG:
1. A high-quality song can be stored in 100kb or less
2. These files are unthreatening to the RIAA, since you can't trivially "rip" music from a copyrighted CD
3. The formats are patent-free and easy to understand
There is an established community of people who have been building software tools and composing tracker music for over two decades:
http://en.wikipedia.org/wiki/Tracker
Examples of some great tunes:
http://www.xs4all.nl/~mon/download.htm
WinAmp is a freeware media player that can play them:
http://www.winamp.com/player/
Currently it's very awkward in SL to make a satisfactory music box, player piano, merry go round, etc. Tracker music is the solution!