Comfy
Comfy is a fun 2D game engine built in Rust. It's designed to be opinionated, productive, and easy to use. Inspired by macroquad, raylib, Love2D and many others, it is designed to just work and fill most of the common use cases.
 
GameSalad
A game engine to build 2D games with no code.
 
Mach
A Zig game engine & graphics toolkit, for building high-performance, truly cross-platform, robust & modular games, visualizations, and desktop/mobile GUI apps
  SGDK
SGDK is a free development kit allowing development of software in C language for the Sega Mega Drive.
  Love2D
A free and open-source framework to make 2D games in Lua
 
Murder Engine
A pixel art ECS game engine built on top of MonoGame.
 
Polygonjs
A procedural, node-based design & animation tool, for the web
 
DragonRuby 2D Engine
DragonRuby Game Toolkit is a professional grade cross-platform 2D game engine
  Three.js
An easy to use, lightweight, cross-browser, general purpose 3D library
 
openFrameworks
An open source C++ toolkit for creative coding.
 
ENIGMA
ENIGMA is a free development environment geared towards game development and compatible with Game Maker projects
  ZGB
ZGB is a Game Boy / Game Boy Color engine that lets you write your own games in C or ASM.
 
Construct 3
Construct 3 is a powerful and user-friendly game development engine without the need for extensive coding knowledge
  MEG-4
Very performant fantasy console with lots of features and multiple languages
  Oxygengine
Oxygengine is an all-batteries-included kind of engine, focused on being Web-first but slowly moving more into more platforms such as desktops and consoles
  App Game Kit Studio
Vulkan powered cross-platform coding
  Storm Engine
Game engine behind Sea Dogs, Pirates of the Caribbean and Age of Pirates games
 
RPG Maker MZ
A new iteration of RPG Maker that let anyone regardless of skill level make an RPG
 
Blitz3D
Blitz3D is al older, DX7-Based Dialect of Basic. Its sports an easy level of entry but can still get relatively powerful with practice.
 
microStudio
microStudio is a free, open source game engine online
 
Chickadee
Chickadee is a game development toolkit for Guile Scheme, providing all the essential tools that parenthetically inclined game developers need to make games in Scheme.
 
Gosu
A 2D game development library for Ruby and C++, with few dependencies and great to learn Ruby or for short game development competitions
 
HaxeFlixel
A cross-platform game engine built with Haxe
 
SnaX
SnaX is a fast and lightweight development tool for 3D-graphics applications based on a real-time, visual programming concept
  Ambient
A runtime for building high-performance multiplayer games and 3D applications, powered by WebAssembly, Rust and WebGPU
 
C4 Engine
Battle tested game engine with visual scripting for 3D games
 
MiniGL
A game library for Ruby based on the Gosu library. Offers helpers for animations, physics, input, UI
  Simple
An editing tool, language, and runtime for creating gameplay using a mouse-driven scripting tool
  Tetra
Tetra is a simple 2D game framework written in Rust. It uses SDL2 for event handling and OpenGL 3.2+ for rendering
 
DOME
DOME is a framework for making 2D games using the Wren language.