Open source VIII engine implementation in C# working on Windows and Linux (Android and iOS planned too!)
C++ game engine for Windows, macOS, Linux, iOS, tvOS, Android, and web browsers
Blueshift is a cross-platform 3D game engine implemented in C++. it's free, open-source, and works on Windows, macOS, iOS, and Android. The project is currently in an early stage of development.
A cross-platform, open-source, pure C game engine for mobile game.
The Wolf is a comprehensive set of C/C++ open source libraries for realtime rendering, realtime streaming and game developing
Lightweight and modular C++11/C++14 graphics middleware for games and data visualization
An open source, cross-platform game engine designed for indie developers.