For the past few years Google has been expanding its reach in the realm of operating systems, quickly attracting users and developers alike by releasing the source code under open source. It started in
2007, with the unveiling of Android, a mobile operating system running on the Linux kernel. Android has been available as open source since October 21, 2008 (Google opened the entire source code under an Apache License, which allows vendors to freely add proprietary extensions without submitting those back to the open source community). Now, Google is gearing up to directly compete with Microsoft's Windows OS with Google's Chrome OS.

On November 19, 2009, Google demonstrated an early version of its Chrome OS, an open source operating system designed to work exclusively with web applications. For consumers who primarily use
their computers for accessing the Internet, Chrome OS's minimalist interface could prove to be an attractive alternative to Microsoft's Windows. Google also released Chrome OS's source code under open source licensing as Chromium OS.

A quick review on open source: Open Source licensing is a response to today's Copyright Laws. The distribution terms of open source software must allow free redistribution, the production of derivative
works, free distribution of the license with the derivative works, and the license must not place restrictions on the software that is being distributed (unlike copyleft, which gives every person who receives a
copy of a work permission to reproduce, adapt, or distribute the work as long as any resulting copies or adaptations are also bound by the same copyleft licensing scheme).

Google plans to release a publicly available stable release of Chrome OS during the second half of 2010.

Sources:
http://www.nytimes.com/2009/11/20/technology/companies/20chrome.html?_r=1
http://en.wikipedia.org/wiki/Android_(operating_system)
http://en.wikipedia.org/wiki/Google_Chrome_OS
http://www.opensource.org/docs/osd