Keeping the ball afloat game-multiple users pressing a button to keep a ball in the air and see how long they can keep it up.
Two piles, pushing a button will remove one item from a pile and add it to the other. Users decide how they want to balance the piles.
Chat function-create a story: two users make a story one word at a time alternating turns, you can view the stories and vote for which you like.
Blind Mad Libs- people log onto the site and are presented with a box to input a verb, adjective, adverb, noun, etc. Then after all the blanks had been filled they can view the story with what other people have inputted.
Similar to idea two, large group of people on land and you can press a button to put them on a boat. If you put too many on the boat it sinks and resets.
The screen is a color, you control the amount of red, green, blue in the image by pressing buttons, as well as the tint/shade.
Virtual garden: people water the plants and provide sunlight. Plants die if they are neglected for too long.
Snake game: multiple people controlling it a la twitch plays pokemon, but much harder.