iTunes on PandaBoard/Raspberry Pi or other single board computer
The primary obstacle to getting a full featured program like iTunes to work is running OS X on non Apple hardware and/or Windows on ARM. 

I do run ubuntu on a Beagle Black and it is suitable for music streaming and light video streaming using open source packages. Nothing I have found works as well as an AppleTV and iTunes Match for music streaming, though. The black CPU is dual core, but severely resource constrained so it can generally walk or chew gum but not both.