Two players knocking on ten points of deadwood or less.
The two-player rummy, and the sharpest game in the family. You do not lay melds down as you go; you keep everything hidden until you knock.
A 52-card deck. Ten cards each. One card is turned up to start the discard pile.
Cards not part of any meld are deadwood, and their total is what matters. Court cards count 10, aces 1, number cards face value.
Draw the top of the stock or the top of the discard pile, then discard one card. Melds stay in your hand — nothing is laid down until the hand ends.
When your deadwood totals 10 or less, you may knock: discard face down, lay out your melds, and show your deadwood.
Your opponent then lays out their own melds, and may lay off any of their deadwood onto yours.
You score the difference between the two deadwood totals.
Knocking with no deadwood at all is gin. You score the difference plus a 25-point bonus, and your opponent may not lay off against you.
If the opponent's deadwood turns out to be equal to or lower than yours, they undercut you: they score the difference plus a 25-point bonus instead. This is why knocking at exactly 10 against a careful player is a bad idea.
Game is 100 points, with bonuses for the winner and for each hand won.