This is a silly one, but also a relatively little-known site...
The pitch: draw a picture from a random prompt using MS Paint level tools in 10 minutes. Someone describes your picture, and someone else draws from that description. Down it goes in a chain until everyone has either drawn something or described something.
You can create "private games" when you reach a certain level (Level 3, I believe), wherein you can invite 6, 12, or 15 people to participate in that private game.
You can see all the pictures and prompts at the end of the game. The spirit of the game is like "Pass the message" where you start with a prompt and watch the message get distorted as it goes down the line. Usually, the result is entertaining. And no, you don't have to be good at drawing.
Seriously, it's fun. These are recent games between newbies. Notice the intentional misreading and misinterpretations. And note that any given person only has access to the one panel (whether drawing or prompt) before them.
Game between vets (people who own Wacoms and level 15+)