"the nintendo ds is an excellent platform for homebrew audio software - here’s an (incomplete) list of some of the excellent sound toys that are available for the platform." Awesome. More listed in the comments, too.

"Shredz64 is a modern day game for the Commodore 64... [its] design is modeled against the popular "Guitar Hero" series, geared toward the ability to play along to your favorite C64 music on the guitar." Plays any .SID file you throw at it. Impressive!