Open source clone of the Age of Empires II engine
Powerful, mature open-source cross-platform game engine for Python
Free, open source game engine online
A retro game engine for Python
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
A refreshingly simple data-driven game engine built in Rust
A pure Go game engine
3D game engine/framework in C, with Luajit and Python bindings now
Pycraft is an open-source, OpenGL based game made in Python
Opensource crossplatform Fallout 2 game engine writen in C++ and SDL
GemRB is a portable open-source implementation of the Infinity Engine
Tools and Z80 engine for creating adventure games.
A game engine for console based text games
Go 3D Game Engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Python ctypes module for the Irrlicht Engine SDK
KlayGE is a cross-platform open source game engine
Open source, moddable game engine for the "Polygon Love 2" game
Scripting language of the hawk game engine
Browser game engine