- 3DWorld (C++, GPL-3.0, mature)
- adventure engine (Lua, MIT, mature, inactive since 2013)
- Aether3D (C++, zlib, beta)
- Alimer (C++, MIT, beta)
- Ambrose3D (C++, zlib, beta, inactive since 2007)
- AndEngine (Java, Apache-2.0, mature, inactive since 2013)
- AnKi 3D engine (C++, 3-clause BSD, beta)
- Anura (C, C++, zlib, mature)
- Arcane-Engine (C++, MIT, beta)
- Atomic Game Engine (C++, MIT, mature, inactive since 2018)
- Backbone Game Engine (JavaScript, MIT, beta, inactive since 2016)
- Bacon2D (C++, MIT, beta, inactive since 2018)
- Bladecoder Adventure Engine (Java, Apache-2.0, mature)
- Blitwizard (C, C++, Lua, zlib, beta, inactive since 2015)
- boardgame.io (JavaScript, TypeScript, MIT, beta)
- C3DE (C#, MIT, beta)
- Cafu Engine (C++, MIT, beta, inactive since 2018)
- Candle (C, MIT, beta)
- Castle Game Engine (Pascal, LGPL-2.0, mature)
- CETech (C, C++, CC0, beta)
- Chunk Stories (Kotlin, Java, LGPL-3.0, beta)
- ClanLib (C, C++, zlib, mature)
- Classic RBDoom 3 BFG (C, C++, GPL-3.0, mature)
- CorEngine (C, zlib, beta, inactive since 2015)
- CroftEngine (C++, Python, LGPL-3.0, beta)
- Crown (C, C++, Vala, MIT, beta)
- DarkPlaces (C, GPL-2.0, mature, inactive since 2014)
- Dedalus (JavaScript, GPL-2.0, beta, inactive since 2018)
- DelverEngine (Java, Custom, mature)
- DesktopAdventures (C, LGPL-2.1, beta)
- dim3 (C, MIT, beta, inactive since 2014)
- Dingo-Engine (Java, 3-clause BSD, beta, inactive since 2016)
- DirectX12GameEngine (C#, MIT, beta)
- Do It Yourself Doom With SDL (C++, MIT, beta)
- DOOM (C, Custom, mature, inactive since 2012)
- DreamZZT (C, C++, GPL-2.0, beta, inactive since 2007)
- Dreerally (C, C++, Custom, beta)
- Duality (C#, MIT, mature)
- DwarfCorp (C#, MIT, mature)
- eAdventure (Java, C#, GPL-3.0, mature, inactive since 2014)
- Elysium Engine (C, GPL-2.0, beta, inactive since 2006)
- Enduro2D (C++, MIT, beta)
- erampage (C, GPL-2.0, beta, inactive since 2015)
- Esenthel Engine (C, C++, Custom, beta)
- ezEngine (C++, JavaScript, MIT, mature)
- Falltergeist (C++, GPL-3.0, beta)
- FIFE (C++, Python, LGPL-2.1, beta)
- Flare (C++, Java, Python, GPL-3.0, mature)
- Flex Engine (C++, MIT, beta)
- Fractal Engine (C++, MIT, mature)
- Free Hero Mesh (C, JavaScript, Public domain, beta)
- Free in the Dark (engine) (C, C++, GPL-2.0, beta)
- FreeSO (C#, MPL-2.0, beta)
- Freya Game Engine (Java, LGPL-2.1, beta, inactive since 2002)
- Fusee (C#, Python, MIT, beta)
- GameCake (C, C++, Lua, MIT, mature)
- gamekit (C++, C, zlib, mature, inactive since 2015)
- GamePlay (C++, C, Apache-2.0, mature, inactive since 2016)
- gist-txt (JavaScript, MIT, mature, inactive since 2018)
- GNU Chess (C++, GPL-3.0, mature, inactive since 2017)
- GNU Go (C, GPL-3.0, mature, inactive since 2011)
- Godot Card Game Framework (GDScript, AGPL-3.0, mature)
- Grail (C++, Lua, GPL-3.0, beta, inactive since 2013)
- Grit Game Engine (C++, Python, MIT, beta)
- Haxima (C++, GPL-3.0, beta)
- HGE (C, Haskell, zlib, beta, inactive since 2013)
- Hypatia (Python, MIT, beta, inactive since 2016)
- ika (C++, Python, PHP, C#, GPL-2.0, beta, inactive since 2007)
- Innocence Engine (C++, GPL-3.0, beta)
- INSTEAD (C, Lua, Java, MIT, mature)
- Intersect (C#, MIT, GPL-2.0, beta)
- ioquake3 (C, GPL-2.0, mature)
- Isogenic Game Engine (JavaScript, MIT, mature)
- Jake2 (Java, GPL-2.0, beta, inactive since 2006)
- JavaScript Graphic Adventure Maker (JavaScript, MIT, mature)
- JediOutcastLinux (C, C++, GPL-2.0, mature)
- JFDuke3D (C, GPL-2.0, beta, inactive since 2005)
- JGame (Java, 3-clause BSD, mature, inactive since 2012)
- KeeperRL (C, C++, GPL-2.0, beta)
- Kiwi.js (JavaScript, TypeScript, MIT, mature, inactive since 2015)
- KlayGE (C++, GPL-2.0, mature)
- Korax' Heritage (None, ?, mature)
- LambdaHack (Haskell, 3-clause BSD, beta)
- Librelancer (C, C#, MIT, beta)
- LimonEngine (C, C++, LGPL-3.0, beta)
- LionEngine (Java, GPL-3.0, mature)
- LITIENGINE (Java, MIT, beta)
- MAGE - Matthias Advanced Game Engine (C++, GPL-3.0, beta)
- melonJS (JavaScript, MIT, mature)
- Metaforce (C, C++, MIT, beta)
- mini2Dx (Java, C#, Apache-2.0, mature)
- Monofoxe (C#, MIT, mature)
- MxEngine (C++, 3-clause BSD, mature)
- neoGFX (C++, GPL-3.0, beta)
- Nuvie (C, C++, Lua, GPL-2.0, beta, inactive since 2018)
- Odamex (C, C++, GPL-2.0, beta)
- ONScripter (C++, GPL-2.0, mature, inactive since 2020)
- Open Cube (C++, C, zlib, beta, inactive since 2017)
- Open Game Engine (C++, LGPL-2.1, beta, inactive since 2008)
- openage (C++, Python, GPL-3.0, beta)
- OpenBOR (C, C++, 3-clause BSD, mature)
- openc2e (C, C++, LGPL-2.1, beta)
- OpenGothic (C++, MIT, beta)
- OpenJK (C, C++, GPL-2.0, beta)
- OpenKeeper (Java, GPL-3.0, beta)
- OpenMW (C++, GPL-3.0, mature)
- OpenNFS (C, C++, MIT, beta)
- OpenRW (C, C++, GPL-3.0, beta)
- OpenSAGE (C#, LGPL-3.0, beta)
- OpenTESArena (C++, MIT, beta)
- OpenTomb (C, C++, Lua, LGPL-3.0, beta)
- OpenVIII (C#, MIT, beta)
- OpenXRay (C++, Lua, ?, mature)
- Oreon Engine (Java, GPL-3.0, mature)
- ouzel (C, C++, Objective-C, 2-clause BSD, beta)
- Oxygen Engine (C++, C, Apache-2.0, mature)
- PainTown (C++, Java, Python, 3-clause BSD, mature)
- Pentagram (C++, GPL-2.0, beta, inactive since 2018)
- Permafrost Engine (C, Python, GPL-3.0, mature)
- phpRPG (PHP, GPL-2.0, beta, inactive since 2006)
- PixelLight (C, C++, MIT, mature, inactive since 2012)
- Plasma (C++, Python, GPL-3.0, mature)
- Playir (C++, Apache-2.0, mature, inactive since 2014)
- Q-Gears (C, C++, GPL-2.0, beta, inactive since 2015)
- Quartz Engine (C++, 3-clause BSD, beta)
- RadixEngine (C++, zlib, mature)
- RBDOOM-3-BFG (C, C++, GPL-3.0, mature)
- ResidualVM (C++, GPL-2.0, beta)
- Rigel Engine (C++, GPL-2.0, beta)
- RogueSharp (C#, MIT, mature)
- rpgboss (Scala, JavaScript, AGPL-3.0, beta, inactive since 2017)
- rRootage (C, 2-clause BSD, beta, inactive since 2004)
- Ruby-warrior (Ruby, MIT, beta, inactive since 2012)
- RuZZT (Rust, MIT, beta)
- Sanity Engine (C++, MPL-2.0, beta)
- ScummVM (C++, GPL-2.0, mature)
- Serious Sam Classic (C++, GPL-2.0, mature)
- sfall (C++, C, GPL-3.0, mature)
- SGE Game Engine (Python, LGPL-3.0, mature, inactive since 2017)
- Sludge (C, C++, Objective-C, LGPL-2.1, mature)
- Solarus (C, C++, Lua, GPL-3.0, mature)
- Spartan Engine (C, C++, MIT, beta)
- Spring (C++, C, Lua, GPL-2.0, mature)
- Squiffy (JavaScript, MIT, mature)
- SteveTech1 (Java, MIT, beta, inactive since 2019)
- Storm Engine (C++, GPL-3.0, mature)
- Stratagus (C++, GPL-2.0, mature)
- sundog (C, C++, Python, MIT, beta)
- Tabletop Club (GDScript, MIT, beta)
- Tapir (C, Ruby, Apache-2.0, MIT, beta, inactive since 2017)
- The Eternity Engine (C, C++, GPL-3.0, mature)
- The Force Engine (C++, GPL-2.0, beta)
- Thunder Engine (C++, Apache-2.0, beta)
- TIC-80 (C, Java, C++, Lua, MIT, beta)
- Torque 2D (C++, C, MIT, mature)
- Torque 3D (C++, C, MIT, mature)
- twin-e (C, GPL-2.0, beta, inactive since 2015)
- Twine (JavaScript, TypeScript, GPL-3.0, mature)
- TwinEngine (C, GPL-2.0, mature, inactive since 2015)
- Tyger (Python, ?, beta, inactive since 2016)
- VASSAL (Java, LGPL-2.1, mature)
- Wagic, the Homebrew (C++, C, Objective-C, 3-clause BSD, beta)
- WebFun (TypeScript, MIT, beta)
- Wintermute Engine (C++, C, MIT, beta, inactive since 2013)
- World of Might and Magic (C++, LGPL-3.0, beta)
- xygineXT (C++, zlib, beta)
- Yet Another Engine (MoonScript, Java, Lua, MIT, beta, inactive since 2016)
- Yorg (Python, GPL-3.0, beta)
- ZGB (C, Assembly, C++, MIT, mature)
- Zod Engine (C++, ?, mature, inactive since 2018)