It’s an ARM processor, so it will run the usual suspects. Linux, Android, etc.
Here’s a page with links to SD card images: http://www.raspberrypi.org/downloads
and Adafruit has a distro, based on Raspbian, called Occidentalis: http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/occidentalis-v0-dot-2
So, yeah, it can run a “real os” on all 64 of them if you wanted. Not the best bang for the buck, but still pretty cheap, if you want to get into clusters.
From : Make Raspberry Pi Section