Since I started looking at React, I've wondered whether it would be possible to create a multi-user game. The game would look a little like a Spectrum game that I used to play called Trans-Am. I'm guessing most people reading this are not going to be old enough to remember this. Essentially, it marks the peak of car game development, and everything has been down hill ever since.
If you have no idea what I'm talking about then there's a demo of the game here.