Making my brain hurt

[Goodmush]

I am thinking about building a world with three moons and wondering what the effect it would have on the tides and the cultures that would develop. Also how it would affect the flora and fauna? I has some ideas but wanted some thought on this.

[OldLace]

Dotting because I am incredibly interested in this. Sorry I can't help, don't know much about astrophysics.

[Lincoln Hills]

When it comes to tides, three moons are easier to hand-wave than two - assume that the lunar effects are usually in opposition and the world has very erratic but weak tides... then assign a few times every decade when the three moons are in conjunction and there are very powerful, possibly even catastrophic flood tides. Such tides might produce wide regions of bayou or salt flats along any non-mountainous coastlines, and drown all low-lying islands altogether. These floods would be a great excuse for long-lost treasure or ruins to be revealed as the seawater recedes.

The tidal stresses may also result in more vulcanism than Earth has: don't be afraid to put in zones of hot springs, regular lava flats, chains of dormant volcanoes and (in parts of the world) more earth tremors. I believe multiple moons also strengthen a planet's magnetosphere, but I don't know if that would affect anything the players would notice...

You might want to give each moon its own symbolism, as Tracy Hickman so famously did in Dragonlance. A small moon on a high-speed inner orbit, crossing the sky with visible speed, might be associated with travel or messengers: a moon with oceans is likely to be associated with life or fertility. Here's a fun possibility: maybe the inhabitants of your world believe that each moon is actually an Elemental Plane - that the sun is a Fire Moon and the other three are Earth, Water and Wind Moons.

I wouldn't go overboard designing odd animals and plants that take advantage of the different tides and magnetosphere - a couple for flavor would be sufficient. As far as adapting existing monsters for your setting, the only major concern I can think of is the effect on lycanthropes: if they transform when any moon is full they'll go berserk at unpredictable intervals, while if all three moons have to be full, they'd hardly ever do so. Both interesting results, but if you'd rather play them as they normally appear you're best off tying their transformation to one particular moon.

[Brambleman]

Tie different lycanthropes to different moons. They transform when "their" moon is full. Will be fun if there is a conjunction.

[Drejk]

This is one of the cases where it is simpler to go with magical/deific astro(meta)physics that trying to be scientifically accurate. Unless one has enough astrophysics knowledge.

[Goodmush]

I like the idea of catastrophic flood tides. It gives the reason to use some of the water based monsters that I rarely get to use. Cities made out of coral and winding sea caves. options just spring to life.
I had been mulling over the seismic activity due to increased gravitational stresses, so that works in nicely. witch brings me to the more mundane, in such a violent world would the denizens develop more into a nomadic culture or with the prevalence of magic construct walls or raise their Cities to negate the need for such defences.
As for the moons I was thinking about linking the transformations to a level of alignment (evil, neutral, good) to a corresponding moon, so giving each moon a different embodiment works quite well with that. But having the transformations triggered by one moon will reduce the work load of timekeeping.

[LovesTha]

Have at least 1 moon that goes the wrong way.

Or maybe have all three on wildly different inclinations (gives better credance to conjunctions being rare and catastrophic)

[Lincoln Hills]

How would cultures adapt? Well, the best way to handle that is to think of every possible solution - then apply those solutions to different cultures. The Western Dwarves might build coastal cities as very temporary wooden structures a few miles from the "main city" (inland and on a hill), while the Eastern Dwarves build incredibly massive stone piers and bastions and winch all their boats high above sea level when a catastrophic tide is expected.

Similarly, the orcs on the north side of a particular volcanic range that spews ash every few years might delight in the ash-falls, wearing full-face masks and goggles and wandering through the forests in search of ash-choked animals and freshly fallen lumps of obsidian: while the lizard folk on the south side of the very same range might have secret, deep caves where they withdraw when their swamps become fouled and gray with falling ash, living below for months until the spring snow-melt cleans out their home.

[Thomas LeBlanc]

You could have each moon have a different symbolism. Good/evil, civilization/savagery, magic/no magic, godly power/power of mortals, etc.

I have never run a world with 3 moons. I did 2 moons, one that determined good/evil and the other was the savage moon. The good moon shined down weakening evil. Fuller the moon, weaker evil was. The savage moon determined the tides and how powerful lycans and animals were.

Both moons are on elliptical orbits. Every 11 years, the good moon would align with the savage moon behind it and all undead have to retreat at least 6 feet underground for 1 hour or be destroyed and was the only time lycanthropy could be cured via a ritual. Every 17 years, the moons align with the savage one closer. That is the only time a lich's ritual could be completed and all lycans assumed their were-form and went on a mindless killing spree.

Once every 187 years, the gods prevent the moons from colliding, but expect a ritual in their honor. If the ritual is not preformed, the gods are unhappy and reign down destruction. They send heralds to the groups they expect to preform the ritual, detailing the rites to be preformed.