I've never seen the tab bar put in the navigation bar before, and I really dig it. I'm actually in the process of designing an education app that plays audio, and have been debating how to avoid a hamburger/basement menu or gestures since the main audience for the app is older, and assumably less tech savvy. Putting the tab bar on top is a clever, and in hindsight incredibly obvious, compromise, since it provides for…
I don't think it's a tab bar in the navigation bar. It just seems to be four buttons on a UIToolbar equally spaced.
Edit: Strange that this was down voted...care to explain why? It's almost certainly not a tab bar. A tab bar switches view controllers. The buttons on this bar present new ones modally leaving the current view controller in place.