Everyone always talks of an "Office" killer, or how something might come along and supplant Microsoft's dominance by Exchange and Windows Server. I don't think this will come anytime soon from the free or open-source crowd. Instead, I think it should come from Google.

A big reason lots of businesses can't or won't move to a gmail/gcalendar collaboration system is because everything would then sit on Google's servers. This becomes a liability risk for the business. But what if you could have Google's offerings running on your own server in your own datacenter?

What if Google offered their initial collaboration tools (email, calendar, contacts, tasks) as an installable suite? They could offer it as a package to run on a linux server, or even offer an appliance like their search appliance. Stick it in your rack, hook it up, configure, and you're set! I think companies would flock to this if it was a reasonable substitute for the Exchange setup. It would be perfect if they opened it up to allow IMAP and/or POP3 access, too, so users could use desktop clients as well. Google, are you listening?