Setting specific houserules

[nolongerchaos]

So what are some of the most fun/interesting houserules you've seen at the table that have been setting specific?

I once had a game wherein casters could learn/use core spells freely, but in order to be able to use a non-core spell you needed to be taught the spell by an appropriate Outsider. The game never got off the ground, but I still love the idea of Wizards, Clerics, Sorcerers, and Druids summoning Fiends, Celestials, Dragons, Fey, etc. to enhance their magical prowess.

[Story]

The last campaign I was in had an elaborate system of houserules for arcane casting where each area had affinities with 5 elements while mages had elemental stats and had to roll in each area to cast a spell, several related feats, plus various modifiers to the checks and everyone was required to have an elemental familiar.

Luckily, the difficulties were set low enough that you could autopass them with even minimal optimization, so it never once actually came up in game. The only real effect was to prevent trading away your familiar.

[MadGreenSon]

I've gutted the system of the Dragonmarked Houses in Eberron, made it so that there are 19 houses currently in existence and de-coupled the basic (Least, Lesser, Greater, Siberys) Dragonmarks from feats/classes and made the progression of those into a separate mechanic. I've also made the Dragonmarks non-exclusive to each house/bloodline.
All Dragonmarked bloodlines can display any of the Dragonmarks, but each house has a pronounced tendency toward one or maybe two.
The system of Guilds leans less heavily on one House per Guild and more on two or three Houses working together in a sometimes uneasy alliance.

I also removed the lightning rail, but that was more personal taste than a house rule.

[nobodez]

Well, most of the campaigns I run I integrate at least a bit of house rules.

For my Eberron game, it was because I used the ethergaunts and a Dungeon adventure to bring in mirror versions of my party, and with them, firearms (eventually there was a whole invasion of Khorvaire by the ethergaunts and their technomagical empire that ended when the PCs got to 20th level and defeated the leader of the empire).

For my Patherfinder Dragonstar game, it's a whole truckload of house rules, from Fame and Prestige, to Armor as DR and Wound Points. It's pretty much a melding of Pathfinder, Star War, Dragonstar, and d20 Future.