"Winner: YouOS, launched in 2005 by refugees from Oracle but still in alpha mode, lets you surf the Web via a browser-within-a-browser window, read RSS feeds, create text documents, and use a Nintendo game emulator to play titles like Donkey Kong.
It's mostly a playground for developers right now, and it isn't very fast, but it is free--and running, say, Zoho Writer inside a Web browser that runs on an outside server through a browser running on your PC is oddly thrilling.
Runner-up: EyeOS is an open-source, free application that comes with a full-featured word processor, a basic calendar, a rudimentary Web browser, and an RSS reader. You can use the hosted version of EyeOS or install it on any Web server. Like YouOS, however, it runs slowly.
Also-ran: By contrast, Desktoptwo relies heavily on Flash and Java to pull off its desktop imitation. Though it supplies no browser, the desktop includes a full suite of OpenOffice applications, an MP3 player, and Adobe Acrobat Reader, and it offers a 1GB virtual hard drive."