For those of you that don't want to outsource Exchange or work with the Google, Mozilla might be a solution for you. They have a nice collection of services that you could re-brand as your own.
OpenPGP message encryption and authentication from Thunderbird (the Mozilla email client) and SeaMonkey for the privacy types. Makes you look like an ally and the expert.
There is a LookOut plug-in that allows ThunderBird to interface with Microsoft.
Instabird is an instant messenger/chat app that also does twitter!
Mozilla has a calendar - stand-alone and a client for Thunderbird. The Lightning calendar has a Google calendar sync add-on.
It might be a way to own the desktop.