▶ Assets
>Images/Art
https://pixabay.com/
>Sprites/Textures
https://opengameart.org/
>Music
https://pixabay.com/music/

▶ Making Engines
>SFML (Full suite)
https://www.sfml-dev.org/
>Vulkan (Extra low-level graphics)
https://vulkan-tutorial.com/
https://github.com/SaschaWillems/Vulkan
https://www.khronos.org/registry/vulkan/specs/1.3-extensions/pdf/vkspec.pdf

▶ Engines
>FOSS
https://castle-engine.io/ (2D/3D Game Engine, Cross-Platform)
https://love2d.org/ (2D Game Engine in Lua, Cross-Platform)
https://www.renpy.org/ (Visual Novel Engine, Cross-Platform)
>Proprietary
https://www.yoyogames.com/en (3D Engine)
https://rpgmaker.net/ (2D/RPG Engine)

▶ Tutorials
>GoDot Tutorial (Simple 3D/2D Platformer)
https://www.youtube.com/playlist?list=PLda3VoSoc_TSBBOBYwcmlamF1UrjVtccZ
>GoDot RPG Tutorial
https://www.youtube.com/playlist?list=PL9FzW-m48fn2SlrW0KoLT4n5egNdX-W9a
>Unity Tutorial (General)
https://www.youtube.com/watch?v=gB1F9G0JXOo
>PS1 Style Game in Unreal Engine 4
https://www.youtube.com/watch?v=JecxUlkXnMo&list=PLHZBDxLlh16vEVYMcWhASW8vREbVHa7V2
>Metroidvania Game in Unity
https://www.youtube.com/watch?v=wJb_NJ1x8XE&list=PLyVF7UrIzKrl1eEipJGd-w9U3ssq5qKPq
>RenPy Tutorial
https://www.renpy.org/doc/html/quickstart.html