The goal of the game is to find the set of 3-7 cards that, when added up, contain an even number of each color of dot.
Check out the Wikipedia page for more info.
You should be able to use cargo run. It listens by default on port 3000.
Everyone can load up the same page; it should work for anyone to find a set and click submit. It's a little hacked together, so if the pages aren't in sync just reload. Everyone is playing the same game at the same time.
Score isn't kept right now, because the server has no sense of a unique player.