Roundcubemail vs Zimbra vs ???

Based on simplicity of configuration and usage, I'd say Roundcube wins by a long shot. Roundcube is PHP based, while Zimbra uses its own proprietary Ajax toolkit. Roundcube is also geared toward pure webmail and IMAP/POP3 configurations. Zimbra is positioned as a more robust solution with calendaring and document collaboration tools, but all the additional tools do require more system resources.

@TheTechStewart:

Based on simplicity of configuration and usage, I'd say Roundcube wins by a long shot. Roundcube is PHP based, while Zimbra uses its own proprietary Ajax toolkit. Roundcube is also geared toward pure webmail and IMAP/POP3 configurations. Zimbra is positioned as a more robust solution with calendaring and document collaboration tools, but all the additional tools do require more system resources.

Can you argument on "proprietary Ajax toolkit"?

What is the backend language? Java or PHP?

I don't have enough development experience to really dig into details, but you might be able to find more answers on Zimbra's features page.

https://www.zimbra.com/open-source/features

Ajax indicates that Javascript is handling the backend.

+1 for zimbra, it is pretty cool