The Symbian Foundation's Symbian^3 is now open source.
Samsung's i8910 Omnia HD smartphone runs the Symbian OSThe Symbian OS is found on almost half the smarphones in the world and it is now all in the open source realm. That doesn't mean you are going to be reprogramming your phone with a custom instance of Symbian but has the potential. Other limiting factors such as cell phone providers tend to discourage that at this time. Still, having access to the operating system source code and associated libraries makes application development and debugging easier. Symbian is also found on mobile devices and being open source means Symbian is a viable platform for new devices.
Symbian targets ARM processors like Texas Instruments' OMAP found in the Samsung i8910 Omnia HD quad-band GSM/GPRS/EDGE handset with tri-band UMTS support. Being open source, Symbian can target other platforms as well.
The Symbian Foundation hosts the Symbian^3 (S^3) operating system and library source code. The project still has work ahead of it. Symbian was originally developed using closed source tools. The current open source platform has significant components that can be compiled using open source tools and the next major release should have all of the platform handled by open source tools. This will put it more on par with Linux and other open source operating systems.
The latest version includes a number of changes including user interface advances like multi-touch gesture support, easier navigation with a new feature-rich homescreen. It also has better networking support, 2D and 3D graphics acceleration for games and applications, HDMI support (High-Definition Multimedia Interface), plus music store integration.
Symbian compares well with other popular open source platforms like Andriod and Symbian will likely compete in areas such as mobile devices where Android is being used. In fact, Symbian may have other advantages for open source developers compared to Android since all of Symbian is open source.