Monogame is impressing and open source, also for PS4 development. Also Xamarin is awesome if you're into .NET.

MonoGame is rough code with a rough build system and a lot of strange behavior. Frequently undocumented, too. I would suggest investigating FNA (a significant fork of MonoGame used in 40+ shipped titles) instead; I have had my tangles with its primary developer but the code quality is significantly improved and it's really worth your time. Doesn't support the PS4, but you can code to the XNA baseline and then hack around MonoGame for the PS4 later.

Is this the FNA you're talking about? https://fna-xna.github.io/