A good use for a Raspberry Pi - Missile Control
My brother gave me what will likely be one of the best useless-but-oh-so-fun gifts ever—a Dream Cheeky Thunder USB foam missile launcher.
The launcher can be used with an extremely boorish app for Mac or Windows... or you can control it with some basic USB communication! I've found a few projects which allow the launcher to be controlled via any OS with Python fairly easily: