You mean for the PlayStation? That is a FreeBSD fork, probably chosen over Linux because of the license.

Nintendo is an interesting example though. According to Wikipedia they actually use a proprietary microkernel, which, if I'm reading this right, I think they developed themselves. Looks like the only open source components they have is some networking code which is published under the BSD license.

https://en.m.wikipedia.org/wiki/Nintendo_Switch_system_softw...

	▲	raggi 7 days ago \| parent [-]
		Yeah, the various docs and presentations given by reversers on the details of nintendos os really showcase a lot of good design choices. An impressive amount of work for just trying to enforce a harder IP moat around entertainment software.