While Microsoft might have the coolest OS setup for its Xbox One, containing a mixture of Windows and Xbox sauce, Sony has opted for an excellent base itself: FreeBSD 9.0. This has been revealed thanks to a couple of leaked screens of the GRUB 2.0 interface on the second-generation PlayStation 4 development kit. While these screens could easily be faked (it's a matter of editing the plain-text GRUB configuration file), it does seem likely to be true. The PlayStation 3 used an OS called CellOS which has always been rumored to have been based on FreeBSD as well.
With its move to an x86 architecture, Sony's decision to use FreeBSD likely wasn't a hard one to make. On the flipside, with so much PC architecture under-the-hood, I can't help but feel like its encryption might be cracked a lot quicker than it was on the PlayStation 3. Of course, off-the-shelf consoles are not going to have an accessible GRUB menu like this, so that's a challenge to work around.
As Phoronix points out, what makes the adoption of FreeBSD interesting is that AMD doesn't have an official Radeon driver for the OS, and the open-source driver is hardly able to handle the tasks the PS4 will require. It seems evident, then, that AMD has worked with Sony to craft up a special driver. Will that mean we'll finally see an official driver for BSD, then? Likely not. We can assume that Sony specifically licensed a proprietary driver, because it wouldn't want it to be easily decompiled by those trying to understand the PS4's workings better.
Given its Unix base, it'd be neat if the PS4 returned the "Install other OS" functionality that the PS3 originally had, but it seems obvious that Sony doesn't want to go down that road again.