In order to test out a generic Python multiplayer game library that I'm working on, I had to come up with a game design for the simplest possible multiplayer game. I'll post the library's code here another time when it's stable and tested, but in the meantime here's the game design that I came up with:
It's a two player turn-based strategy game with the simple objective of destroying all of the other player's ships. There are two phases; the input phase, and the simulation phase. Each player runs the client on their own computer and they input their next moves simultaneously during the input phase. The moves are hidden from the other player until the simulation phase, which happens once both players are finished inputting their moves. Control of the ships is simple; click the blue circle and then click the playing field in order to define the path of each of your ships for that turn; click the red circle and click in the direction which you'd like the ship to shoot for that turn. When ships are hit with enemy fire their health bar will show up with it's value diminishing, and when it gets to zero the ship will disappear. You can also see the health bar of ships by hovering the mouse over them.