Your only weapon in Door Knocker is a deceptively harmless door. To get from room to room you have to place this door into a wall, an action that will create a hole in the wall between connected rooms. It's kind of magic. But, as you explore, you notice that rooms quickly become filled with bullet-spewing turrets, and G-Men-style agents wearing sharp suits and firing guns.
How do you defeat them? Well, you telekinetically grab the door, and punt it towards your enemies, by physically kicking it around the room. Physics! 'Knockabout physics fun' is probably the best way to describe this wonderfully silly action game. You have a door, a foot, and a load of baddies to knock it into, over and over again. Here's what that looks like, via Warp Door:
For more great free experiences, check out our roundup of the best free PC games.