Masterwork has added monsters, races, items and reactions such as sewing, repairing(?) and crafting gear from bones etc.
Also there are "spells" you can craft, basically you make some kind of stone or arrow that has a syndrome on it which you then throw away. The fire arrows are especially potent. This uses and trains your concentration skill I think.
In addition to this the warlock race has a special interaction you can do depending on which type of warlock you decide to start out with. Its basically a vapor or gas cloud attack you can do pretty often with a syndrome or temperature that afflicts on contact.
Be aware that they have currently unactivated much of the armors and stuff to drastically reduce lag in fort mode, but if you go into the entity_"race name" then you can change them back into active, as well as add some of the weapons/armor that usually only appears in fort mode on rare monsters. Perhaps theres even a check for it on the launcher, Im not sure. Its pretty apparent which lines you should change anyway.
Ive personally modded my own game so that there are two more races. One with 4 arms and 4 legs, they live for a loong time but they have a ratio of 10:1 women and the children take 85 years to grow up. Second one with only one weak hand, but four strong legs a horn and a stinger which all can inject a weak syndrome upon attack. They grow up quickly but a large portion of the race become bandits. Both of these build cities just like humans which you can visit. Its really not that hard to mod in new civs when you got a blueprint and then just go wild with it and change basically everything.