This is not really a well thought out response. Most businesses don't have the resources to employ a system administrator to manage their Windows install, let alone manage all the other services required to run to meet the same level of functionality that "ready to go" services like Google Apps provide. Seriously.
Does anyone have a current best-of-breed list of web enabled applications (preferably open source) that you could run on your own server? Ideally, I'd like to put together a kit that is easy to install, either on your own server or on any hosted provider. Bonus points if the kit includes replication tools built in so that you can use multiple web hosts, and have your own redundant cloud.
Derek, this would be a cool project. If someone could work alongside a talented UX/Designer and bundle together some open source software with a nice UI, that would be quite useful. Roundcube seems to be taking a pretty good stab at this.