For those of you who insist on the TL,DR version of everything, here you go.
There is no TL,DR version.
TIRRA is a continent and several related islands on a planet roughly earth-like. It is elf, dwarf, and orc-free. There are three races of humanoids and three races of lycanthropes. It has nearly twice the area of the North American land mass, as well as extreme terrain, new creatures and plants, politics, and… Well, sorry. That’s all you get for a TL,DR section. You’ll just have to start reading.
What’s so different about TIRRA?
The main difference is that you’re not going to find iron or steel. There just isn’t any to be found. Most of the iron that is available is from meteorites, and these bits get used as compass needles, magnets, or door stops. Iron is so uncommon that steel has not been developed. Iron is smelted into cast iron, but this is brittle – meaning that iron really isn’t of much use anyway.
Technology therefore is the science of what is possible with this planet-wide handicap. There is no steel to support an industrial revolution. The people here are smart enough to figure it out, but there just is no iron available.
Since you’re going to ask, yes! The planet has a magnetic field, and that’s a good thing for navigation and keeping the solar radiation out. If you want to find the source of the magnetic field though, you’ll have to dig an extremely long way down into the core of the planet where molten iron is available.
This lack of steel will influence your choice of weapons, armor, friends, and other attitudes. Things that you may have done in other game environments need a nudge in a different direction in TIRRA.
Is there magic?
Yes, moreso in some areas than others. Some areas of Tirra are very technology (tinker) centric and they have developed clockworks, small steam engines, and anything from music boxes to devious traps – all based on physics, chemistry, or some other branch of learning. Other areas of Tirra are very magic (wizard) savy, and magic and alchemy are preferred, as are all the old ways.
To which era from earth’s history can Tirra be compared?
The closest approximation is probably the Renaissance. Art can be very realistic. Music can be very complicated. Buildings can be full of surprises and a variety of building materials. Politics, intrigues, and a tension between magic and technology. And don’t forget the four churches and their interests!
Is Tirra steampunk?
Not exactly, though in some areas it can be played that way within the limits of available resources. The rule of thumb (subject to your game referee’s guidance) is that if Leonardo Da Vinci could conceive of it, you can try to build it, buy it, or use it. Most brass, bronze alloy or copper versions of things that may come to mind may be heavier or more cumbersome than you’d like, but there is no iron available – so get over it already.