KlayGE is a cross-platform open source game engine with plugin-based architecture.

Note: development continues in stuntrally3. 3D racing game based on VDrift and OGRE with own Track Editor. The main repository with Stunt Rally 2.x sources and data.

C++ game engine for Windows, macOS, Linux, iOS, tvOS, Android, and web browsers

The Dæmon game engine. With some bits of ioq3 and XreaL.

3D FPS game engine with full dynamic lighting and shadows

An advanced C++ 3D game engine powering an in-production game yet to be announced

SMK - Simple multimedia kit - C++ WebAssembly

Easy to use cross-platform 2D game library for C++

Lightweight game engine.

GoldSrc engine plugin for 3D sound

A C++ prototyping engine that is striving for an easy to use API, hiding all the dirty details so that you don't have to care.

plugins for theora video playback and openAL audio

Igneous is an open source game engine written in C++.

A 2D game engine written in C++

now at:

Lost Astronaut's Game Creation Framework: A massive 1800+ class 1400 file extravaganza of OpenGL, WinAPI, OpenAL and many other features, written in Visual Studio for over a decade!

Game engine playground.

C++/OpenGL implementation of a classic arcade game "Breakout"

OpenAL EAX Extension

Mhat'S Engine attempts to be a safe, simple and fast cross-platform 2-D multimedia engine written in C++20 for MSVC++, Clang and GNU C++ Compilers. It brings together many OSS libraries into one easy-to-use environment controlled by the LUA interpreter with the aim to operate on WinXP+ (x86/x86-64), MacOS (x86-64/Arm64) and Linux (Ubuntu x86-64).