We seem to be mentioning both Parallels and Kerio pretty frequently, and they keep coming up with cool stuff. Kerio announced today that it will be offering its mail and collaboration platform, Kerio Mailserver, as a Virtual Appliance for Parallels on the Mac, news that will be of interest to a lot of folks looking for an even easier way to get away from Exchange.
The Virtual Appliance comes with a preconfigured version of CentOS 5.3 Linux, optimized for Kerio Mailserver. It looks like an ideal solution for businesses that need to run more than one OS, allowing hardware to be shared and making efficient use of server power.
I'm guessing you'd want an XServe or high-end Mac Pro if you're planning to deploy multiple Virtual Appliances, but I would think that the KMS Virtual Appliance should run on any Intel Mac which can do a decent job of running Parallels to begin with. If you missed it, check out the WWDC video of a tricked-out Mac Pro running Leopard and two installs of Vista with Parallels.
The Kerio Mailserver Virtual Appliance comes ready-to-run (if you have Parallels Desktop or Server) as a 30-day trial. Pricing starts at $499US for ten users, with an option to add integrated McAfee Anti-Virus for an extra $100US ($599).