Car door bumpers
I'm not a scientist or inventor of any kind but it does make me mad when I park in a crowded parking lot and I come back to my car to see a ding in the side of it from someone opening their door and hitting it. This idea is very simple but it might help. Some type of pad you can put on the side of your door to keep other doors from hitting it. All it has to be is padding on a magnet. You can just stick the pad to your car when you park with the magnet. Then when you leave, you can just take the padding off and throw it in your car.
Reward: Free product