Godot is a fully featured, open source, MIT licensed, game engine.
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
An advanced flexible game engine for Java.
An online multiplayer turn based strategy game and board game engine.
A Lua Game Engine
Egret is a brand new open mobile game and application engine
Jetpac Clone, written in JavaScript, wrapped in a Mac App
A massively multiplayer turn-based strategy game engine
Mahasona engine is an open source game engine.
Gorgon Game Engine (GGE) is a C++ game engine that handles many tasks.
Simple and low-consumption Java 2D Game Engine
Java decentralized cross-platform network multiplayer game engine
XNA based game engine completely written in c#
Built to be ease of use, with no programming knowledge, Multi-platform
Simple, component-based game engine based on Ogre and PolyVox,
A runtime-programmable, cross platform, game engine
Open Source 3D Game Engine
A roguelike game engine/editor