Interesting. I considered doing something like this after getting frustrated with the typical game engines. I wanted to make a grand strategy game, but utilizing an MDI style UI as I knew I could focus on building out the game itself without having to put too much effort into designing the UI within whatever engine was being used and just embed a graphics library for drawing the actual game visuals.
I had some trouble getting the embedding to work quite right, but I might try an pick the project up again sometime.
I know I’ve seen other games use this UI style before, but I haven’t heard of the one you posted, and can’t recall whatever game is hidden in the back of my mind. Command: Modern Operations comes to mind, but is a bit fancier.