Linux: While the main idea behind Chrome OS is pretty cool, you may not want to limit yourself to only web apps. Peppermint Ice is a Linux distribution that is based on web app usage, but allows the installation of native apps.
Peppermint Ice is based off Linux Mint, but designed to be a fast-booting, web app-launching Chrome OS competitor. Its default browser is Chromium, and it contains shortcuts to all the same web apps, like Facebook, Seesmic and the Google Suite, but also contains apps like Transmission and Dropbox, which are just plain better as native apps.
While, of course, you could mod any Linux distribution to act like this, Peppermint Ice comes pre-configured for those that want a hassle-free experience. If you want to add a shortcut to any other web app, Peppermint Ice has a built-in tool to do so. In fact it's easy enough to use that even non-Linux veterans can figure it out pretty easily. If you tried Chrome OS and found that it was a bit too minimal, Peppermint Ice may be just your speed. Hit the link to try it out.