I've always wanted to run a D&D game with several groups of players, all members of a thieves' guild breaking apart after the death of the guildmaster. The top contenders for the position decide to have a Great Game to determine the next guildmaster. Each faction has one month to steal as much loot as possible. At midnight on the last day, they are to meet at a shady warehouse to value their hauls and crown a new guildmaster.
The game sessions would consist of the players planning heists & cons, spying on the other factions, and trying to steal from each other.