Run It Twice
Dealing the remaining board cards twice in an all-in pot and splitting the pot between the two runouts.
When two players are all-in, they can agree to deal the rest of the board twice — two turns and rivers, or two rivers — with half the pot riding on each. Some games run it three times, a third of the pot each. Both players must agree; either can decline. High-stakes cash games made it famous; plenty of home games allow it now too.
The key fact: running it twice changes nothing about your expected value. If you're a 65% favourite in a $400 pot, your expectation is $260 whether you run it once, twice, or twenty times. What changes is the distribution. Run once, and you take $400 or $0. Run twice, and the most common outcome is a chop — $200 each — with the sweeps pushed to the extremes. Same average, much narrower swing.
So when should you? Bankroll logic. If the pot is trivial against your roll, run it once and save two minutes. If the pot is a real chunk of your bankroll — the $2,000 all-in at the end of a big home-game night — running it twice is the rational choice even though neither option is "free". You're buying variance reduction at zero cost in EV, which is worth doing exactly when the variance can hurt you.
Set house rules in advance: is running it twice allowed, how many times maximum, and does it need both players' consent (it should). Note also the cousin mechanic — insurance — where instead of splitting the runouts, one player pays a premium to guarantee a payout. Same goal, worse pricing. Tournaments never allow it, incidentally — running it twice is purely a cash-game courtesy between two consenting stacks at the table.