Here's a demonstration of the lightweight game music engine we use in World's End.

While developing Chapter 1, we were limiting ourselves to 20 MB to avoid running into size limits on game portal sites.
Once we decided upon the game's length, we quickly ran out of space for music even using unacceptably low MP3 quality.
Fortunately, since we compose in Renoise — a music tracker — we were able to find a playback library and figure out a conversion process to switch from pre-rendered audio to dynamic sound generation.
Thanks to the .XM support provided by Flod, we got our hour-long soundtrack into 1.8 MB for a total size of 7.8 MB for the entire game.

We're working on the soundtrack for Chapter 2, and decided to give a long overdue shout out to Christian Corti and Photonstorm for creating Flod and helping liberate our game music from the horror of lossy compression.

Software Used:
Renoise - Composition
Xrns2XMod - Conversion to .XM
MilkyTracker - Finishing
Flod - Playback in Flash
SiON - Reverb
Electrixion - Visualization