What I like about Zimbra is its open sourceness (natch) and its intelligent approach to information presentation as applied to email and calendaring. Think Gmail but with tight integration with a web-based calendar, and with a lot of neat little information integration bells and whistles — like generating a contextual menu from a phone number in an email with an option to place a VoIP call. AJAX is no mere hot buzzword here but is well applied such that mousing over bits of data can generate tooltip-style boxes with related information, such that rolling over a date will pop up any items on your calendar for that day, e.g. Also slick, it understands relative terms like "tomorrow" or "next Tuesday" and will popover relevant calendar details for those terms. What's exciting about this is that it eliminates a sizeable portion of the need to keep switching back and forth between panes, interfaces or applications to access information you've always felt should be available to you from right where you are.

The email portion has conversation grouping functions like Gmail, as well as tagging. I worry that the tagging interface will grow cumbersome for those of us masochists who tend to have as many tags as we have del.icio.us links — at that point dragging and dropping an icon for each tag we want to add just doesn't make enough sense to make the transaction cost worthwhile. This is the same reason I hate the tagging interface in iPhoto, where one must physically click and drag to associate tags with photos, one by one. Still, Zimbra's overall approach to email and calendaring is downright refreshing.

[Via Ajaxian]