Back in June we mentioned on Phoronix that the PS4 was reportedly running a modified FreeBSD 9.0 platform. Not everyone believed the report and there were no large statements out of Sony trumpeting the FreeBSD operating system.
However, for those that missed it, this Sony Computer Entertainment page mentions all of the open-source software used by the production PlayStation 4. On that web-page, the FreeBSD Kernel is listed along with some of the other FreeBSD software components.
Other open-source software worth mentioning that's used in the PlayStation 4 is the Cairo library, eglib, libcompiler-rt, libcxxrt, libjpeg-turbo, Lua, Mono VM & Class Libraries, the Pixman renderering library, and WebKit.
While there's this open-source software on hand, and Sony does comply with the licensing, the PlayStation 4 is still not a very open console. For Linux gamers interested in an open-friendly game console, the best bet is surely with Steam Machines running the Debian-based SteamOS.