Blazium Engine is a free, open-source fork of Godot for building cross-platform 2D and 3D games and applications, with the tools, platform integrations, and improvements you need.

Butano is a modern C++ high level engine for the Game Boy Advance.

Recoil is a battle tested open-source RTS engine that, allied with a flexible Lua API, allows you to implement the perfect UI and mechanics for your game with the ability to support thousands of complex units simultaneously.

An engine designed for development teams (C++/C# programmers, 3D artists) working on interactive 3D apps

Free software game engine focusing on developing games faster

Redot Engine is an open source fork of Godot with the goal of fulfilling the promise of Godot.

A free and open-source, cross-platform game engine for creating 2D and 3D projects with Lua or C++. It is lightweight and promotes the simplest way to use the best performance of a data-oriented design.

3D game engine with lua scripting

Luanti (formerly Minetest) is an open-source, cross-platform voxel engine, inspired by Minecraft. Primarily written in C++, utilising the Irrlicht Engine, and it provides an API for users to make games or mods, for existing games, using LUA.

Dagor Engine and Tools source code from Gaijin Games.

A lightweight, multiplatform, free and open-source 2D game engine

A Lua based game engine with focus on ease of iterations and usage

Luminoveau is an open-source C++ game engine designed for simplicity and reach — 2D and 3D, desktop to console, from your first game to your next release.

A free, all-in-one, cross-platform game engine that makes it easy for you to create 2D and 3D games.

Flecs is a fast and lightweight Entity Component System that lets you build games and simulations with millions of entities.

Carimbo is a lightweight 2D game engine written in modern C++. It features Lua scripting and is designed for high-performance deployment across all major platforms.

An open-source real-time 3D engine

A full-source code available and agile game engine

Unreal Engine enables game developers and creators across industries to realize next-generation real-time 3D content and experiences with freedom, fidelity, and flexibility

The AGS Editor is a Windows-based IDE for creating adventure games as quickly and easily as possible.

Axmol Engine is an open-source, C++ multi-platform engine designed for mobile devices, desktop, and Xbox, well-suited for 2D game development.

A 2D-oriented, data-driven, portable game engine focused primarily on ease of use and powerful features

Tomb Engine is a reimplementation of the Tomb Raider engine, for the creation of custom levels.

Cute Framework (CF) is a framework available for making 2D games in C++. It provides a portable foundational layer for building 2D games in C/C++ without baggage, gnarly dependencies, or cryptic APIs.

A scene-oriented, flexible 3D engine written in C++ designed to make it easier and more intuitive for developers to produce games and demos utilising 3D hardware

An open-source, completely free-to-use engine for realtime 3D games, visualizations, simulations, experiments

A next-gen game development platform designed to empower developers and artists.

Matali Physics is an advanced, modern, multi-platform, high-performance 3d physics environment intended for games, VR, AR, physics-based simulations and robotics.

A powerful, C++ engine, built on literal decades of proven torque technology

This is a cross platform toy engine that is available on Linux, Windows and MacOS.