VGLeaks reports that the operating system used on Sony's upcoming PlayStation 4 is called Orbis OS, and is a modified version of FreeBSD 9.0. So far it's unknown if Sony plans to bring back the much-loved "OtherOS" it pulled from the PlayStation 3, which allowed other operating systems like Linux or FreeBSD to be installed on the system.
In a separate report, Phoronix points out that it's better to use FreeBSD over Linux, as the former has more liberal licensing. But given that the console is using an AMD eight-core APU with Radeon GPU cores, there isn't a Catalyst driver available for any BSD operating system. Even more, the open-source driver ported over from Linux with Radeon KMS and Gallium3D is still in a primitive state.
Of course, there probably is a Radeon driver for the PlayStation 4's FreeBSD-based OS given that the console's APU is a joint effort between AMD and Sony. That, or AMD ported the Catalyst code-base to BSD. We'll find out more once the console arrives in our hands and gets ripped apart.
Discovery of the console's OS was based upon a second-generation development kit for the upcoming console. The report was accompanied by several screenshots taken after booting up the dev kit. The pictures reveal that the operating system will allow developers to load up in console mode or graphical mode, the latter of which is what consumers will see on the retail side.
The images go on to show some of the files and directories in the development kit, including SceSysCore.elf and its shared library of files with the *.so file extension. Unfortunately, that's it for now, but the batch of screenshots can be viewed and studied here.
The last we heard, the PlayStation 4 is scheduled to hit the market around November 13, 2013. It could be sooner than that here in the States given that the date was discovered in Europe, but Sony could easily have decided to set a global date instead despite its previous launch history with consoles.