What is Urho3D engine?
Urho3D is a MIT licensed open-source lightweight, cross-platform 2D and 3D game engine implemented in C++. 

The name Urho means hero in Finnish.
Where can I download it?
You can download and install Urho3D by following the instructions on their website - https://urho3d.io/docs/getting-started/quick-start.
I'm confused, it says to use Docker and I don't know what that is. Can you just give me step by step directions to install it? I am using Ubuntu Linux. Also, what is Docker even?