Some very interesting project is just starting, a developer named winocm posted that he’s successfully ported the iOS Darwin kernel to ARM devices, the whole testing process was done on his own Nokia N900.
Anyway, there’s no user interface at the moment and the system root filesystem is based on iPhone OS 4.3.5, the source is available at github.com/darwin-on-arm.
Here’s the list of the current supported ARM devices:
ARM RealView Emulation Baseboard (ARMPBA8_ALT)
ARM RealView Platform Baseboard for Cortex-A8 (ARMPBA8)