Web-based games:
Newgrounds Game Dev Resources💩,
Web Game Dev (GitHub)
awesome-game-design, awesome-learn-gamedev, Game-Development-Guide
Existing games' technologies:
Awesome-Game-Analysis
Visual novels:
Ren'Py (GitHub)
Web game engine - no-code:
Modd.io (GitHub)
Web game engine - HTML5:
Phaser (GitHub),
PlayCanvas
2D engine - JS:
Construct
2D engine - Lua:
LÖVE ((GitHub)with awesome-love2d)
2D engine - Python:
Pygame (GitHub)
3D engines:
Flax Engine (GitHub),
Godot Engine ((GitHub), with awesome-godot),
Source SDK🆓,
RTS engines:
permafrost-engine
Open-source game lists🆓💩:
awesome-game-remakes,
awesome-jsgames,
awesome-open-source-games,
FLOSS-Games-on-Steam,
OSGL (GitHub),
Open_Source_Games_list,
Open Source Game Clones (GitHub)
Specific open-source game clones🆓💩:
The Dark Mod (Thief),
Freeciv (Civilization) (GitHub),
OpenRA (Command & Conquer) (GitHub),
Widelands (Settlers II)
Unix ASCII games🆓💩:
awesome-ttygames
Licensed games:
Amnesia: The Dark Descent,
Amnesia: A Machine For Pigs,
Command & Conquer/Red Alert
Elite (for the BBC Micro),
Redirection,
shapez GitHub,
The Simpsons: Hit and Run,
Veloren (GitHub),
VVVVVV,
YSFLIGHT (GitHub)
Free licensed games:
0 A.D. (Git),
Citybound (GitHub),
Mindustry (GitHub),
Orbiter Space Flight Simulator,
Space Nerds In Space (GitHub),
The Battle for Wesnoth (SourceForge) (GitHub)
awesome-ai-tools-for-game-dev, awesome-game-ai
Compatibility tool for Linux:
Proton