EGroupware is a enterprise ready groupware software for your entire network. Enables your team to manage contacts, appointments, to-dos and many more for your whole business. It comes with a native web-interface which allows access your data from any platform all over the planet. Moreover you also have the choice to access the EGroupware server with your favorite groupware client (Kontact, Evolution, Outlook) and also with your mobile (smart-phone) or PDA via SyncML.

http://www.egroupware.org/

The leader in next-generation messaging and collaboration.

http://www.zimbra.com/