It's mainly for this forum game called mafia. In the game, there is a town and maifiosi faction. It's the goal of the town to find out who among them is a part of the mafia. During the day (day in the game) , everyone gets to vote for who they want to lynch. Once a majority vote is reached, that person is lynched, their alignment is revealed and they are no longer in the game and the game moves to night. During the night the mafia chooses someone to kill. And the game alternates between day and night until either side wins. Town wins if all mafia are lynched. Mafia wins when they out number town.
There's also lots of other roles like cop which gets to investigate a person each night and is told their alignment. And doctor who can choose a person to protect during the night from a mafia kill.
It's really fun. If you're interested I reccommend you join a game sometime. They have games for new players all the time. I think one is actually about to start up.
And to fully answer your question, dgames also is for other strategy based forum games. Mafia is the main thing though.