Mashup games are always fun. Those built upon FourSquare have an extra layer of enjoyment, because they're tied to the real world. In the case of City Warfare, players use various water weaponry to soak other FourSquare users.
Sulake, social entertainment and games company, has launched the Habbo API for its award winning Habbo Hotel game platform. Developers can publish games onto the platform and studios can utilize the API to access Habbo's social graph and monetization capabilities.