Godot[1] is free and open source, similar to Unity, builds to mobile, desktop and web. It supports 2D and 3D, as well as VR through some addons. It has a built in python-like scripting language called GDScript that's easy to pick up and understand, and you can also use C#, C++ or many other languages through bindings (even Javascript[2]).

It's a really impressive effort for an open source project. There's a channel on YouTube called KidsCanCode[3] (not just for kids!) which has a load of project-based tutorials to build lots of types of games.

[1] https://godotengine.org/

[2] https://github.com/Geequlim/ECMAScript

[3] https://www.youtube.com/channel/UCNaPQ5uLX5iIEHUCLmfAgKg/pla...