Godot Engine – Multi-platform 2D and 3D game engine

Animated sprite editor & pixel art tool (Windows, macOS, Linux)

Emscripten: An LLVM-to-WebAssembly Compiler

This is the official source code of FreeCAD, a free and opensource multiplatform 3D parametric modeler.

Cocos2d-x is a suite of open-source, cross-platform, game-development tools utilized by millions of developers across the globe. Its core has evolved to serve as the foundation for Cocos Creator 1.…

Cross-platform, graphics API agnostic, "Bring Your Own Engine/Framework" style rendering library.

Bullet Physics SDK: real-time collision detection and multi-physics simulation for VR, games, visual effects, robotics, machine learning etc.

Flexible level editor

Simple and Fast Multimedia Library

MAME

LAV Filters - Open-Source DirectShow Media Splitter and Decoders

Industry-standard navigation-mesh toolset for games

OpenVR SDK

An open source, turn-based strategy game with a high fantasy theme.

Doom 3 BFG Edition

Game engine

2D skeletal animation runtimes for Spine.

Direct port of the Bullet physics engine to JavaScript using Emscripten

The 2013 edition of the Source SDK

Half-Life 1 engine based games

Farbrausch demo tools 2001-2011

MIT Licensed Open Source version of Torque 3D from GarageGames

The Atomic Game Engine is a multi-platform 2D and 3D engine with a consistent API in C++, C#, JavaScript, and TypeScript

Doom 3 GPL source release

Improved version of the X-Ray Engine, the game engine used in the world-famous S.T.A.L.K.E.R. game series by GSC Game World. Join OpenXRay! ;)

An open source version of a game engine developed by Croteam for the classic Serious Sam games.

A tiny, hackable BitTorrent client.

ScummVM main repository

A flexible emulator front-end supporting keyboardless navigation and custom system themes.

Cross-Platform Level Editor