Pathfinder 2nd-edition Houserules

Common Rules

All characters have equal XP.
All characters use Automatic Bonus Progression.
All characters gain a Free Archetype.
All characters gain one bonus skill increase at 3rd, 7th, 15th level.
Exploration actions will cause tension dice to be added to the pool. Each 10 minutes, a dice is added to the pool. The pool is rolled, then emptied, when it reaches 6 dice or when someone does something unsafe. If any dice rolls a 1, something bad happens.
When something gives you the right to Stride or Step, you can use any 1-action activity with the [Move] trait. For example, you could use Sudden Charge to Stand and Step; follow up a Shove with Fly; use haste to Tumble Through with a jump spell.

When using elements that are not [Common], you should check with the GM.

[Uncommon] elements are generally allowed. Please use them with some moderation.
[Rare] elements are generally restricted to one per character.
[Unique] elements generally should be obtained in-game.

Official Paizo content is always allowed.
Third-party content and homebrews are generally allowed, but you should check with the GM.
Both Remastered and Legacy content are allowed. A character could even learn both ray of frost and frostbite. If unspecified, Remastered is assumed.

Usually, when PvP happens, players roll as usual, and the defender gets to change the degree of success by one step in either direction. Alice tries to Lie to Bob. Alice rolls Deception (a success!) but Bob changes it to failure, and is not fooled. Alice casts breathe fire on Bob. Bob rolls Reflex (a success!) but changes it to a crit, and takes no damage. Alice casts breathe fire on Bob. Bob rolls Reflex (a failure!) but changes it to a success. Bob has Evasive Reflexes, so it becomes a crit, and Bob takes no damage. Alice tries to Shove Bob away from a foe. Alice rolls Athletics (a failure!), but Bob changes it to a success, and moves away from the threat.
This rule does not apply if PvP is unintentional or unfortunate. For example, Alice casts breathe fire on a pack of zombies, and Bob is caught in the blast.
This rule is adapted from the sidebar on Gliminals, a monster forcing you to damage your allies to prevent death by over-healing.

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Dual-Class PCs Gestalt

A classic very-high-power game. Most likely used at low player counts.
Note that because Dual-Class characters already get two class feats every even level, this rule generally replaces Free Archetype.
Pushed Rolls from Call of Cthulhu

Outside of combat, when you fail at a roll, you can decide to push your luck. You must describe another way that you retry, giving it all you have. This allows you to reroll the initial failed roll. However, should you fail again, you automatically get a critical failure. You cannot push a roll again until another player pushes a roll.
Connections from Traveller RPG

A character can become Trained in a bonus skill at 1st level. It must be a skill that is related to, or used in, a shared history that this character has with another player character in the same game. Work with other players to create those stories, which happened off-screen, usually before the start of the campaign.