Inside Mac OS X 10.5 Leopard Server
Information Week goes into some detail about what's new in Mac OS X 10.5 Leopard Server.
The list details items that have been publicly posted and are not amongst the "secret" features Steve Jobs claims they are holding back, but does provide an interesting summary of the upcoming server operating system.
The features include iCal Server, Wiki Server, 64-Bit capabilities, File Services, Web Services, QuickTime Services, iChat Server 2, Mail, Xgrid 2, and Open Directory 4.
These features are detailed on Apple's Leopard Server Sneak Peak pages.