Zimbra has created a communication and collaboration suite, all open source. They've been around for some time now, and have shown big progression towards a serious candidate on the office market. last time I reported about Zimbra, I focused on the fact that it's performance was poor on older hardware.

Today the company today announced that it has passed four million paid hosted and on-site mailboxes. mentiones that Digg, Mozilla andthe University of Bern Switzerland are amongst Zimbra's clients. When I gave Zimbra a testdrive some time ago I was quite impressed with it, besides the fact that I personally think it has way too many features. But then again, maybe that's what clients (businesses) need or want. And apparently this is the case, since their clientbase is growing. I think Zimbra has become a serious player in the office market, and it could easily serve larger companies very well.