Tim Bray: What’s Going On?:

Check out the architecture; this is a competitor for existing server-side communications products like Microsoft Exchange and Sun’s Messaging Server. It also has a decent-looking AJAX front-end, inspired mostly by Outlook but with what seem to be cool integration hooks (Rich Sharples wonders whether JavaScript is really the right tool for the job). Anyhow, good luck to Zimbra

(Via PlanetJava.org.)