Title says it all. They released it early this morning, and it works exactly how you think it should. Doesn't require ps plus, the free version works the same as it does on computer and tablets, you can play music while playing a game (which turns of the music in game, but keeps dialogue/other SFX on), and you can control it from another device. I don't think people are going to care about audio cds on ps4 now. It's also on ps3, not sure if it works the same there.
Edit: Just tried it on ps3. Its laggy as shit and you cant use it when playing a game. So it's kind of pointless on that platform.