We only reimplemented the engine, not the game. You still need to own a copy of Morrowind so there's something for the new engine to actually run. That said, it is possible for it to run other potentially-open-source games, such as OpenMW's example suite (which isn't finished enough to even call a game yet) or the Robowind demo (which I can't remember the licencing details of) .

I have wasted almost as many hours in OpenMW as I have with the official engine. It is just that good.