What are the variants & house rules in Backgammon?

Section 6: Variants & House Rules

The rules above govern sanctioned tournament play. Several widely used conventions are optional and must be agreed or specified by the event:

Automatic doubles, beavers and the Jacoby rule are treated as options rather than defaults (Rule 4.4.11).
Dice on checkers: whether this invalidates a roll is an explicit rule option, not a fixed rule (Rule 4.1.3.4).
Baffle boxes vs cups: both are permitted randomisation devices with different requirements (Rule 3.2.3.2, Rule 3.2.3.3.1).
Chouette: the multiplayer money-game form, in which one player takes on a team of others each holding their own cube. Outside the scope of the tournament rules.
Nackgammon and hypergammon: alternative starting positions used casually; the tournament rules address errors in the standard starting position only (Rule 4.2.1).

The rules above govern sanctioned tournament play. Several widely used conventions are optional and must be agreed or specified by the event:

Automatic doubles, beavers and the Jacoby rule are treated as options rather than defaults (Rule 4.4.11).
Dice on checkers: whether this invalidates a roll is an explicit rule option, not a fixed rule (Rule 4.1.3.4).
Baffle boxes vs cups: both are permitted randomisation devices with different requirements (Rule 3.2.3.2, Rule 3.2.3.3.1).
Chouette: the multiplayer money-game form, in which one player takes on a team of others each holding their own cube. Outside the scope of the tournament rules.
Nackgammon and hypergammon: alternative starting positions used casually; the tournament rules address errors in the standard starting position only (Rule 4.2.1).