A few months ago, I found out about the "Darwin on ARM" project. This tries to take the Darwin operating system and port it over to ARM processors. Here's some insight on the project.

Supported Hardware Configurations:

• ARM RealView Emulation Baseboard with Cortex-A8 CoreTile
  
• ARM RealView Platform Baseboard for Cortex-A8
  
• Samsung S5L8930X (Apple A4 – iPhone 4 GSM/CDMA/RevA, iPad 1, iPod touch 4G, Apple TV 2G)
  
• Samsung S5L8922X (iPod touch 3G)
  
• Samsung S5L8920X (iPhone 3GS)
  
• Texas Instruments OMAP3530/3730 (BeagleBoard xM)
  

The current state:
"The kernel does boot past IOKit initialization and can start a usermode process. Validation of a simple binary that calls write() using standard UNIX syscalls did succeed. It also can boot from a multitude of booters including Apple’s own iBoot (albeit a very old revision of it). It also can additionally start launchd and actually execute dyld proper now. launchd now dies after forking, but hey, it’s a start."

The project is dual-licensed under the BSD and APSL licenses.

The entire thing is on GitHub: http://github.com/darwin-on-arm/xnu

Source/more information: http://winocm.com/xnu/projects/research/...us-of-xnu/