Written tutorials and books on Unity Game engine
The only written tutorials I can find for Unity game engine are the following two sites:
As for books, a great free PDF beginner book I found is at:
As for other books, I found the best publisher that seems to keep up with the new Unity versions is https://www.packtpub.com/ I also chose this publisher as it also sells quality videos or you can buy a subscription, the books and videos cover useful areas like optimisation and Artificial Intelligence, something I find often lacking on sites like YouTube as most the tutorials are often basic here. Additionally https://www.apress.com/ have some good written books on the Unity Game Engine as well as O' Reilly Publishing.