25: Favourite Revolutionary Game Mechanic
Listing these because they made the games involved stand out, and their effects can be seen in later games. (I already mentioned the use of Jenga in Dread but it hasn’t affected later games substantially.)
Marvel Super Heroes (FASERIP): Karma. Want to succeed at something but think the dice will be against you? Spend Karma. If you succeed anyway, lose a token amount. If you fail, spend enough after the fact to bump up to success. Never pin all your ideas on a single roll and mess up again. Beautiful.
Ghostbusters: Dice pools. Grab a bunch of a common die type and roll them. The better you are, the more dice you have. Wild swingy results get evened out.
Adventure!: Dramatic Editing. Taking out-of-game bennies like Karma a big step further, to give the players a graded level of control over the narrative around their characters. The founding of great game-specific examples like Drama Points in Buffy and Flashbacks in Leverage.
Doctor Who (Vortex): Initiative based on action. Talking always goes first, then running, then doing anything else except fighting, then fighting.