Out of all the Microsoft products, I am the biggest fan of Exchange Server. Exchange is a messaging and collaborative technology, developed by Microsoft and its latest incarnation, Microsoft Exchange 2007, works beautifully with the entire range of Office Suite. Microsoft Exchange also features the "Direct Push" technology, wherein email and other items are synced in real time on Windows Mobile devices. In other words, Exchange is a truly unique product and there are practically no direct competitors to it in the market.
Exchange is mostly targetted at corporate environments, however, its feature set is best suited for any average user, due to the seamless integration between the client and the server portions, intuitive UI and support for various kinds of access (desktop client, web, mobile). There are various other reasons, and I will let this amazing blog post do the explanation. Since it is practically impossible for a home user to run an Exchange server environment due to hardware, bandwidth and licensing cost constraints, a whole bunch of companies offer, what is known as "Hosted Exchange" environment. I personally run an Exchange server on a virtualised environment, mainly for test and learning purposes, however, I am looking into switching to a hosted environment. There are many players out there, but I am looking at Sherweb's single-user friendly offer. If I do end up trying them out, I will put up a future blog post detailing my experiences.