MabiWeb
This is a play-by-web site that offers the possibility to play boardgames with other people via Internet, in a turn-based (not real-time) system. The site provides a graphical interface where players can see the game and execute their actions. The system keeps track of the game status, enforces legal moves and notifies players by email when it is their turn to move.
Users need to be registered in order to play, but registration is totally free, the only requirement is a valid email address.