Android
Android has quickly become a very important player in the mobile space. Over the past 4 years it has grown from nothing to become the leading smart phone operating system (http://www.gartner.com/it/page.jsp?id=1622614). This puts it ahead of iOS, Blackberry, Symbian and Microsoft’s mobile OS.
It has a pretty interesting history as well. Android started off as a company that was developing a mobile OS. In 2005, Google purchased the company and it wasn’t until 2007 that anything related to the acquisition was announced.
In 2007 the Open Handset Alliance was formed. It is a group of companies whose mission is “to accelerate innovation in mobile and offer consumers a richer, less expensive, and better mobile experience. Together we have developed Android, the first complete, open, and free mobile platform.”
The Android OS is built on top of Linux and is (almost) completely open source meaning that it can be modified and distributed freely.
The Android OS itself utilizes Java but not Sun/Oracle’s Java, a different implementation so that Google or whomever does not have to pay Sun royalties. The same goes for the development of Android applications
More Information:
Dalvik: how Google routed around Sun’s IP-based licensing restrictions on Java ME