I'm a huge fan of Zarafa, a full Outlook/Exchange replacement with MAPI, Web access, iCal, and ActiveSync support. Zarafa recently became notable because the company open sourced its e-mail alternative to Microsoft Exchange/Outlook., but I'll admit to being very impressed by
I spent some time with the Zarafa demo and assuming it administers as nicely as it operates for the end-user, it's a winner. Is it better than Zimbra? After all, Zimbra also has iCal, Web access, ActiveSync, etc.
It's hard to say, given that I wasn't able to put Zarafa through a full workload like I do with Zimbra each day in my work. I think the Zarafa interface is a bit cleaner than Zimbra's...
...but one of my primary reasons for loving Zimbra is the Zimlet, making it super-easy to integrate Zimbra with third-party services and applications. (One of my solutions engineers integrated Alfresco with Zimbra in a week.) Zarafa? It is still an island of productivity, not an archipelago of connected islands like Zimbra.
Even so, it's good to see competition in this critical market segment. Despite all the hype around Twitter and other "Web 2.0" communication tools, e-mail is still the crux of enterprise communication. The more robust open-source e-mail alternatives to Exchange, the better. Welcome to the party, Zarafa.