Lady Squee said
The easiest way to learn is to play it. It's really complicated to explain. Jorick did a great job of explaining it before the site crashed. If only we still had it. =/
Oh, but we do. I saved that shit for future use. :D
The core premise of Rabbit Doubt is simple: there are non-killers (rabbits in the original version) and killers (wolf, snake, and so on in the original). The killers have the simple goal of staying hidden, surviving, and killing everyone else to achieve whatever the win condition of the game is (as decided on by the game manager), be it only killers left standing or only a certain number of players left alive that the killer(s) can then eliminate in one fell swoop and achieve total dominance. The non-killers have to find out who the killers are and deal with them before they're out of time/people to get the job done.
There are typically a lot of special roles involved, the amount and nature of them depending on the game manager's preference and imagination. Roles that you'll almost always see (aside from the killers) are a Mayor who is elected by the players at the start of the game and receives some benefit or power, Detectives who can investigate others to learn their roles, Protectors who can defend others from the killers, a Matchmaker who can pair two players together at the start of the game so that if one dies the other goes with them, and a Doctor type who can save targets of killers or sometimes straight up revive the dead. Other roles can range from a Self-Sacrificial role who will take a killer with them in death, to someone who can prevent all role abilities of a target player, to a Vigilante type who can kill others but isn't a murderer that the non-killers need to take care of, and anything else the GM can think up to add to the game. Some roles will be known to exist, but others might be secret to all but the GM and the person with the role, so be wary of shenanigans at all times.
The game is played in turns. There are two kinds of turns: Day Phase and Night Phase; they are sometimes named other things, but their function remains the same. Night Phase is when the primary killer strikes, picking and attacking their victim. There may be many other roles that can act in the night, so there could be a lot more going on than just a kill. The Day Phase is also known as the lynch phase because that is exactly what happens: the players vote to lynch someone that they think is a killer. Whoever receives the most votes is executed, and hopefully they were truly a killer, else the non-killer players have squandered one of their few turns to try to save themselves.
While there might be a lot of discussion in the thread and in private messaging (depending on the rules of the GM,this may not be allowed, so check the game rules before you go plotting and scheming in private) going on, the main way of trying to figure out who the killers are and what the hell is going on comes in the form of story posts. There is a story premise for the games, ranging from the simple "you're a town of rabbits and there's a werewolf monster hidden among you, try to survive," to anything else the GM can cram the premise into (such as the worlds of Harry Potter or Game of Thrones), and that acts as the foundation for the story posts. Each turn's action is written out by the GM into a story post, the posting of which usually signals the end of the turn and comes with an announcement to send in actions for the next turn. The intent of the story post is to give subtle clues to roles, particularly the killers, and show/explain the player actions that took place in that turn. Hopefully they'll also be entertaining for the players to read and make up a hectic but cohesive plot, but that's a bonus rather than a main concern.
Hopefully that was all clear and informative. The TL;DR version is "sign up, get role, read story posts, send in turn actions when prompted, try to win." Good luck.
Also, I'm definitely interested in playing.