The fact that the PS4 runs FreeBSD has been written about extensively. The contributions they've made, less so... mainly because most of the work they did was before they announced that they were using FreeBSD, and they went to significant lengths to avoid that information leaking out (e.g., shell companies were set up so that code could be contributed without revealing the ultimate source).

Probably the most easily identifiable contributions are in LLVM; Sony is one of the largest contributors to that project, and it's entirely due to the PS4.