Zimbra competing with Microsoft Exchange.

MS exchange is currently holding majority share in corporate email and organiser
market.
Our three clients currently holding their own in-house exchange servers to
manage their emails, calendar, contacts and organiser within their organisation.

Zimbra is giving tough competition with some obvious advantages.
Zimbra is first created for web and then extends facility for stand alone
applications.
With its powerful AJAX tools, it allows same features as MS EX at the same time
provides facility such as skype call, VOIP calls, mobile application sync and
corporate mashup.
And all this is at fraction of cost compare to Microsoft Exchange.
(you can get open source copy free of charge)

You may want to visit their website to explore more: www.zimbra.com
Visit demo
here....
Visit admin section demo
here.....