2D game development library for Ruby and C++
Svelto ECS C# Entity Component System
A .NET ascii/ansi console engine written in C# for MonoGame and XNA
Entitas is a super fast Entity Component System (ECS) Framework
Urho3D Game engine
A pure Go game engine
Retro game engine for creating games like it's 1997
Open source reimplementation of GTA San Andreas game engine in Unity
Opensource crossplatform Fallout 2 game engine writen in C++ and SDL
A modern, cross-platform Quake game engine based on FitzQuake.
GemRB is a portable open-source implementation of the Infinity Engine
Orx: Portable Game Engine
A fork of Chocolate Doom with small Quality of Life enhancements
3D Scene Builder
A Tile-based Game Engine written in C# mimicing retro consoles.
Vivid3D is an open-source 3D engine with powerful 2D UI.
A conservative source port of Heretic that is identical to DOS
The world is no longer the same
A conservative source port of Hexen that is identical to DOS
A fork of dhewm3 with an emphasis on modernisation and vanilla Doom 3
Go 3D Game Engine
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.