Rockbox

Rockbox is an amazing microcosm of Linux for the average user. It's got an incredible amount of power, features that the contributors happened to want are already present and are well developed, other features can be approximated by sufficient tweaking and combining of settings, and if you really want a particular feature, go look at the source, buddy.

The crazy thing has Doom, solitaire, and a bunch of other games, including a Gameboy emulator (dust off those ROMs). It has an instrument tuner in it using the microphone.