FAQ - Frequently asked questions by Axel Auweter (2 June 2004)
Roadmap by Michael Steil (23 May 2003)
Michael's Project Log/Diary about his thoughts on the recompiler (20 May 2004)
Apple hosts a well maintained set of documents about Darwin and Mac OS X on their Developer Website.
A description of the PowerPC instruction set by IBM: 6xx_pem.pdf