Like the idea of your machines running a cloud operating system, but you'd rather keep your data and activities local? If so, the eyeOS MiniServer is a download you might want to check out.

It really doesn't get any easier to create a DIY server. Download and run the executable, tick a couple checkboxes, and it's ready to go. Other machines on your network can access the server by opening http://hostname:8080 in a supported browser - Firefox, IE, and Chrome all worked nicely.

The usual basic apps are available: web browser, rss reader, bulletin board, contacts, calendar, word processor, calculator, and notepad. There's even a basic chess game.

Unfortunately, the available version is a bit old. Nevertheless, it's still an incredibly easy way to set up a server to provide the system-in-a-browser experience on your own LAN or WAN. It's very light on resources all the way around: the server only used about 11mb on my Vista x64 machine, and there wasn't a significant increase in Firefox's footprint when running the OS in a tab.
If you're after a bit more information, you can check the MiniServer forum on the eyeOS site. It is, however, largely inactive at this point. Download links in this post point to Brothersoft, as I was unable to find any active links on the eyeOS web site.