The Imaginary Marching Band project is creating open-source wearable musical instruments, which let you pretend to play trumpets, trombones, drums and more with apps like Garage Band.
Unlogo uses video filtering software to detect and replace brand logos. The software is open source, so it can be tweaked for other purposes. Perhaps to obscure adult-only footage? Or video bombs.
Awesome Stuff from Technabob, MightyMega and 95Octane