Microsoft's Windows Home Server is a very unique product, combining features of Server 2003, Vista, Small Business Server and adding some very advanced backup/restore and disk redundancy and disk management technology.
The backups/restores are automatic, daily, and allow you to restore a single file or an entire PC painlessly. You can restore yesterday's copy, or a copy from four months ago. These backups are managed automatically and are done in a very efficient way, minimizing the space required for so many backups.
Disk management is also painless. When you need more storage, you plug in another disk. No need to create or modify arrays. If you want disk redundancy, a mouse-click will enable redundancy at the folder-by-folder level. Unlike RAID, you don't need to make an entire disk redundant if you only need certain folders redundant. There are reports of 20 TeraByte-plus WHS boxes out there.
There's also remote computer and remote file access from the Internet and a full IIS web server if you want.
WHS also monitors itself and its Windows clients. If there's a problem with AV, firewalls, backups, or disks, WHS gives warnings on all the desktops until the problem is fixed.
The whole thing is very simple to install and manage. It's built so the average homeowner can install it with a few mouse clicks. Yeah, it's $100 for the software. That's $20 a year for a typical five-year server life. You can also use the free four-month trials to use it for a while if you wish. Hardware requirements (in real life) are EXTREMELY low. You can pretty much use any PC built in the past seven years for the installation, or you can buy an entire pre-built WHS server from several sources, sometimes for as low as $250 including the WHS software and a 1 TB hard disk.