Interested in a 290-page manual for Mac OS X, written by Apple?
A manual is available from the Apple Developer Connection Web site, called “Inside Mac OS X: System Overview.” The file is available for anyone to download.
Also, there are useful documents for Mac OS X Server users, notably the Netinfo doc, at the Mac OS X Server Web site. Finally, Apple has a Web page devoted to Mac OS X 10.1. It elaborates on points raised during the Macworld New York in July.