We thought about this, however we wanted to focus on game and ideas, not really techniques. I think the best way to have games working at the same time would be to have them connected over localhost with TCP/IP, but that might've been a bit too shady (firewalls and stuff). Shared save would be nice but not really knowing how saving data in browser works (different domains probably would break it), we didn't want to go that way. I am actually very glad that it worked out the "analogue" way.
Cheers, glad You liked the game.