Zynga (Farmville, Cityville) has created Words With Friends Free, a variation on the classic Scrabble board game that allows you to play word games with your friends whenever you want.
Everyone knows how to play: you want to rack up more points than your opponent by placing your letters on a board with different boxes offering point bonuses, until you have as many words down as possible.
Now, the best part of Words With Friends Free is that it has an asynchronous multiplayer system that also allows you to maintain up to 20 different games at the same time. You can take your turn, send it off to your friend, and then they have as much time as they want to respond. So you can take your time figuring out the perfect move.
Some additional features allows you to maintain a chat conversation with other players, and zoom in on the game board to get a better idea of how everything is laid out.
Words With Friends Free is a modern version of an old favorite. It's the perfect game to play here, there, and everywhere.