Actually, Apple makes an iCal server: http://www.apple.com/server/macosx/features/ical-server.html http://www.apple.com/server/macosx/features/ical-server.html

Actually, Apple makes an iCal server: http://www.apple.com/server/macosx/features/ical-server.html http://www.apple.com/server/macosx/features/ical-server.html And Novell GroupWise is the server-side product from that company which does calendaring: http://www.novell.com/products/groupwise/features/#calendar http://www.novell.com/products/groupwise/features/#calendar There are definitely alternatives, depending on what functionality you need.