Full 64-bit operating system
On appropriate systems with 4GB of RAM or more, Snow Leopard Server uses a 64-bit kernel to address up to a theoretical 16TB of RAM.
iCal Server 2 with improved CalDAV support
A new web calendaring application, push notifications and the ability to send email invitations to non-iCal users.
Address Book Server
Provides a central location for users to store and access personal contacts across multiple Macs and synchronized iPhones. Based on the CardDAV protocol standard.
Wiki Server 2
With server side Quick Look and the ability to view wiki content on iPhone.
A new Mail server
Engine that supports push email so users receive immediate access to new messages. However, Apple's implementation of push email is not supported for Apple's iPhone.
Podcast Producer 2
With dual-source video support. Also includes a new Podcast Composer application to automate the production process, making it simple to create podcasts with a customized, consistent look and feel. Podcast Composer creates a workflow to add titles, transitions and effects, save to a desired format and share to wikis, blogs, iTunes, iTunes U, Final Cut Server or Podcast Library.
Mobile Access Server
Enables iPhone and Mac users to access secured network services, including corporate websites, online business applications, email, calendars and contacts. Without requiring additional software, Mobile Access Server acts as a reverse proxy server and provides SSL encryption and authentication between the user’s iPhone or Mac and a private network.