[bluesilver07]

Banshee3D is pretty cool too - https://github.com/BearishSun/BansheeEngine. The vast majority of the work is done by a single person.

[ttctciyf]

There's also Urho3D: https://urho3d.github.io/ "a free lightweight, cross-platform 2D and 3D game engine implemented in C++ and released under the MIT license."

It has an impressive feature list, including: "Cross-platform support using SDL 2.0 (currently runs on Windows, Linux, Mac OS X, Android, iOS, Raspberry Piv1.3 including other generic ARM boardsv1.6, and Webv1.4 with Emscripten toolchain)"

[floatboth]

There's also OpenMW https://openmw.org/en/ which, of course, works best for creating Morrowind-like games :) But you can make completely new games with it.