This Project Zomboid News (PZN) update talks about the 4 main things the devs say Build 42 centers around; that being the animal/crafting update, the map expansion, updating the engine, and a switch from client side inventory management to server side inventory management in multiplayer.
We also get confirmation on a long talked about feature which was unknown if it would come out in Build 42 or 43. You can read all about this update here:
Source: https://projectzomboid.com/blog/news/...