Is there a way to hide the title bar of applications?
I think the short answer is no.

TinkerTool is one of the best utilities out there for modifying the way your system appears/behaves. They do not have any options to remove the title bars from applications in general, although there is one setting to hide the title bar of windows in Quicktime X Player.

The longer answer would be for open-source applications you could potentially modify the code generating the UI.