My personal mod.Not a full conversion mod but it contains quite a lot of changes and additions to the game.

Adds several new creatures
some new necromancer style "secrets" which work so so.
Giants, ettins, and cyclopses are no longer semimegabeasts but an entity of cave dwelling baby snatchers.
A Gorlak entity. Trades during winter, mostly sells cave animals and other cave products. No wagons.
In addition to a bunch of other changes.
The folder contains a "feature log" which goes into more detail.
Due to the nature of this mod I recommend you look through it and take the thing you like and remove the things you don't. Or at least that's how I would use it if I hadn't made everything myself.

1.13
Some special ores and other stones
some new creatures
other edits

1.12
Dryad civilization
Strange weather to some savage biomes
consolidated the magic schools
some new creatures
three new underground plants
added compost ogres

1.10
Some minor changes
One additional creature

1.9
Two more semimegabeasts
An animal source of rock crystals
One underground vermin creature

1.8
Added Birds of fraud
Added haunted toys (these are currently close to indestructible in arena mode so they might need adjusting)
Removed the attempt at adding more species to the goblin civs since 50.12 seems to be addressing that.