One playing field, many players
Playing field is a rectangular grid.
Each player controls a brush which can move with a fixed velocity along each axis. Each player has her own brush color.
A player can start drawing by pressing a Space button and moving the brush.
If a player completes a closed figure, the figure is filled with that player's color.
The goal is to color as much of the playing field as possible.
I only managed to implement a playing field that is more-or-less synchronized across all the players. Enjoy. :)