A couple free & open-source Engines and game frameworks you can use today as alternatives. Feel free to comment with more.
Godot - https://godotengine.org
MonoGame - https://www.monogame.net/
FNA - https://fna-xna.github.io/
SDL - https://www.libsdl.org/
SFML - https://www.sfml-dev.org/
Adventure Studio - https://www.adventuregamestudio.co.uk/
bgfx - https://github.com/bkaradzic/bgfx
armory3d - https://armory3d.org/
ogre3d - https://www.ogre3d.org/
Renpy - https://www.renpy.org/
thanks for all the suggestions so far, I went through all comments (I hope) and gathered them here on a github list so it's easier to share around, feel free to make PR with more things or corrections. There are both free and license based tools on that list now, but all by suggestions so far.
https://github.com/DJLink/list-of-game-engines-and-frameworks/
@ima fixed, thanks
@djlink I saw some people talking about Heaps (and Haxe), but I can't really vouch for it so I didn't bother with a PR.
https://heaps.io/
@djlink pixi.js