This had to happen, Google has entered the OS business. Well, they're not in the Desktop OS business, their strategy is to win the market of the eBooks, those really small and cheap computers aiming at connectivity. The main idea behind this product (Chrome OS) is that people are 90% of their time on the internet. And that... ok they tell it very well themselves, just watch this video:

Done? Ok. It seems quite logical to get to this point. With all the services that we use on internet, most of our data is alreay in the cloud, so this all fits. When I saw Chrome on Windows for the first time, with its task manager, its separate processes for each tabs, its workers (similar to threads, they're part of HTML5)... I realized that the browser was really becoming the new OS. No problems of portability (well almost), your data always available all around the world... The advantage of this approach is that you can then build a really cheap and really fast computer just designed to go on the internet. Google also provided a video live demo:

So this is not the OS proper for now, just the open source project, so that devs can already dive into the code and collaborate or experiment with it. It's all there: the Chromium projects.

Note: I thought I remembered that they already had released somehow a desktop OS, called gOS, but they did not. gOS stands for "Good OS" and is a modified version of Ubuntu with an emphasis on web 2.0 apps and "in the cloud" data.