Aorlis is game system agnostic, and you may run whatever system you prefer when you the game master. But, I would be remiss if I didn’t mention the elephant in the room, Dungeons and Dragons and all the D&D-like games around it. The basic system comes in many flavors from many publishers, and that’s fine.
If you play D&D in Aorlis, there are few suggestions I wold make to keep the gaming experience in tune with the setting. You don’t have to follow these, of course.
In regard to character classes, there is no monk or druid. There are monks or monk-like characters in distant lands beyond the Known World. At this stage in history, those distant characters have not yet been to Aorlis. On the flip side, back when in history a thousand years or so, there used to be druids. They are long gone, and their religion is poorly remembered because the Pagan peoples didn’t write down the tenants of their faith. So, you might find modern Pagans, or forgotten druid groves, or similar things, but the druids themselves are long gone. Bards, also from that forgotten period, did survive and are common enough because they converted to the Faith, or the Universal Church.
There is no Halfling or Hobbit race in Aorlis. Never was. Orcs are likewise non-existent. The reason should be obvious—these races as currently presented are based on the writing of J.R.R. Tolkein. Aorlis is not the Lord of the Rings or Middle Earth. The same prohibitions apply to mithril, balrogs, and other things specific to that fantasy epic. Note, none of this is meant to a slight to Tolkein and his work—I’m a huge fan, and have been all my life.
Elves are different. Aorlis draws upon older, European mythology, on J.R.R. Tolkein’s version of them. The faeries of Aorlis are dangerous, alien, and do not play well with humans. You are certainly welcome to play faeires, or people with faerie lineage, or changelings, but be advised the human population and religious institutions will treat your character as a blood enemy. If you have fairie blood in your family tree, your are well advised to keep it a close secret. There is also no drow race.
The same goes for dwarves. Dungeons & Dragons style dwarfs are rare to non-existent in Aorlis. They can be found in mythology, but actual dwarves are from Faerie and often called Kobalds or Trow. Gnomide hybrids come close, but it’s better to not dwell on that.
Dragons are alive and well, if very rare, in Aorlis. Aorlisian dragons are sourced from medieval European legend, as seen through the Aorlisih an filter. There are no dragon breeds based on chromatic colors, metals, gems, or similar as it is in D&D. Most Aorlisian dragons are green or brown, with hues more in common with serpents.
Aorlis has an extensive bestiary of creatures to draw upon, and most are drawn from European mythology. There are none of the D&D specific creatures like mind flayers, purple worms, owlbears, and the like. These creatures are iconic D&D creations, and that is another world.
There is no planes of existence in Aorlis like that of D&D. The spiritual world, as people in Aorlis understand it, is much closer to Dante’s Divine Comedy.
So, you can’t run a game without elves, monks, druids, red dragons, and mind flayers? No problem. How you make Aorlis and its setting your own is up to you. Your version does not have to match the “official” version. It’s a wild multiverse out there, and which world you choose to run ultimately is up to you. Be creative, and run the game you want to run.