Russian Roulette Mafia
In this setup, players can publically daykill each other at any point. The first daykill has a 1/6 chance of succeeding, the second a 1/5, the third a 1/4 etc. A player may not daykill again until after all other players have made a daykill attempt. There are no nights, and no voting.
The original setup first ran in scumchat consisted of two town-aligned players and one mafia-aligned player. It since been run twice during Marathon Day as a 7 player setup.