The rumor has appeared and spread over the Internet about the PlayStation 4 which tells that PlayStation 4 is running a modified version of the Unix distribution FreeBSD 9.0.
This information is not completely verified, but in fact Sony is not a stranger to the open source community.
As we can all remember for sure, the Playstation 3 has an option called OtherOS which allows users to run Linux system, unfortunately it has been removed later.
The image posted on neogaf.com which has been taken from VGLeaks indicate that the PlayStation 4 runs Orbis OS which is based on the FreeBSD 9.0 system.
The FreeBSD is a free open source operating system, Unix-like which has been derived from Unix of AT & T.