Our sibling makerspace at Chalmers, ETA happens to have a huge Barco projector (we're talking industrial-grade) which you can project some pretty cool stuff with. They had previously projected some memes and recruitment material, but I wanted to create something more interactive.
The backbreaker
I created a mutliplayer fighting game for it. You simply open a webpage on your phone, where you get a gamepad to control your character with. Everything runs in Unity, which runs a web and socket server for hosting and receiving input. The game output is then piped over Spout into VVVV, where most of the look is achieved using shaders and post processing. The projection mapping is also done here.
The game was deployed during the pub crawl, which unfortunately was very cold and empty, but the people who tried it really enjoyed it. I'm actually considering making it into a full game, as it's got a pretty good feel. It's a smash-like, where you knock each other off the stage but with physically simulated swords you need to swing around. You could actually do some pretty good dueling and combos with it, all entirely unscripted.
There was an attempt to make it perspective-correct when viewed from the ground but we didn't have the time to adjust the rendering camera to the right position. So unfortunately the 3D-illusion is a bit broken...
Below is a video showing a player being knocked off the screen. The projected area extend way beyond the actual screen, so you can see the player flying off and onto the rest of the building! This however also resulted in the game area having a very low resolution and brightness.