Dungeon Deities is part Browser-game, part realtime Dungeon Crawler. Players traverse the Dungeons of other players, carefully avoiding traps and battling enemies in search for treasures, which they can then steal. Naturally, you store your loot in your own dungeons, so make sure they are safe!
It's very simple for players to have a variety of events trigger when the hero pushes a button. That can be helpful -- perhaps doors open, or previously impassable tiles can now be walked over -- but it could also be a trap.
And what's more fun than having your friends walk right into your traps?
So put up some torches, make the room look nice, and perhaps name the room something hinting at a trap, and watch as players will become wary to push the innocent "open red doors"-button.
Psychological Warfare. Can be pretty fun.