I've just pushed new sources of Magenta which is my attempt at creating an open source Darwin/iPhoneOS environment based on the Linux kernel. Lots of new fantastic changes. CLI only, no GUI stuff whatsoever. This can also run a lot of frameworks from iPhoneOS (not that you should be trying to do that).
Anyways, enjoy.
Sources:
http://crna.cc/magenta_source.html
Github repo:
https://github.com/christinaa