Urho3D is a game engine made by developers, for developers. The code is clean and well commented.
No String Attached
Urho3D is free and will always be free. There is no hidden royalties. It is IDE-agnostics and has no vendor lock-in.
Urho3D runs on Windows, Linux, macOS/iOS/tvOS, Android, and even on Raspberry Pi. It also runs on your browsers.