A couple free & open-source Engines and game frameworks you can use today as alternatives. Feel free to comment with more.

Godot - godotengine.org
Defold - defold.com/
FNA - fna-xna.github.io/
SDL - libsdl.org/
SFML - sfml-dev.org/
Adventure Studio - adventuregamestudio.co.uk/
bgfx - github.com/bkaradzic/bgfx
armory3d - armory3d.org/
ogre3d - ogre3d.org/
Renpy - renpy.org/

#gamedev

Godot Engine - Free and open source 2D and 3D game engine

Godot provides a huge set of common tools, so you can just focus on making your game without reinventing the wheel.

^{Godot Engine}