It's a form of the uClinux kernal, it's amazing what people have done theese days, I mean, someguy got BSD running on a toaster. I used to have iPodLinux on my iPod when my iPod still worked, but as like the rest of the 4th gen and below ipods my hard drive died on me. It's a pretty cool mod, theres a SNES and Gameboy Color emulator. I personally liked to play Pokemon blue on my iPod
That game seems to never get old....