"Zimbra focuses on solving the cost and complexity for enterprises that run large email/collaboration systems. We accomplish this by combining industry-proven open source components with our experience in designing and operating large-scale messaging and mission-critical software systems, at companies such as Openwave Systems (the leading provider of messaging infrastructure to service providers), Sun Microsystems, Portola Communications, BEA Systems, WebLogic, SEVEN Networks and AOL - About Zimbra"

Sound corporate isn't it? Actually Zimbra is focus on enterprise level. For end user, not really suiteable for you guys. This is really technical part of Zimbra. It's software design for installation at particular server for working together with email systems like Exchange or other corporate mailing systems.

Two options: Network Edition, Open Source Edition.

More Info:
Zimbra
Zimbra Screenshot

p/s: Zimbra is powered by Ajax too!