It's the SockMafia Game format, with a few extras for the new end-of-game functionality that's in beta.
Here's Reverse Mafia as an example. Pay attention to:
- The properties field under each player, that's where scum is marked
- The values field on the game, that's where the winner is marked
- The record of votes
ETA: useless onebox is useless: https://gist.github.com/yamikuronue/10235415d7da1f19345828922f2c96ff