microStudio is a free, open source game engine online

A 2D game development library for Ruby and C++, with few dependencies and great to learn Ruby or for short game development competitions

A cross-platform game engine built with Haxe

SnaX is a fast and lightweight development tool for 3D-graphics applications based on a real-time, visual programming concept

Battle tested game engine with visual scripting for 3D games

A game library for Ruby based on the Gosu library. Offers helpers for animations, physics, input, UI

An editing tool, language, and runtime for creating gameplay using a mouse-driven scripting tool

DOME is a framework for making 2D games using the Wren language.

A mature cross platform graphics engine designed for high performance games. It was used in major titles like Dead Cells, Dune Spice Wars, Northgard and Wartales.

WASM-4 is a low-level fantasy game console for building small games with WebAssembly

Urho3D is a free lightweight, cross-platform 2D and 3D game engine

A simple Lua framework for rapidly building VR experiences

Inform is a programming language for creating interactive fiction, using natural language syntax

A powerful game development platform to create world-class entertainment experiences

A hand-crafted 2D game library in Go

Playscii is an open-source ASCII art and game creation program with Python scripting.

A minimalist Kotlin Multiplaform Game Engine

nCine is a cross-platform 2D game framework written in C++ with an emphasis on performance, but it is also scriptable in Lua for more flexibility. You can use it to create your games and tools or to learn and experiment with its source code.

2D game engine written in Haxe, with a block based visual scripting system inspired by Scratch

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! The project seeks to port to a Linux/Winux environment from Visual Studio.

And engine to make simulations of any kind, ranging from simple prototypes to professional 2D and 3D games, simple physics or graphics demonstrations to robust, realistic simulations

Echo is a game engine which uses many industry-standards for game development

2D Game Engine with Lua Scripting made on top of SFML

A multi-platform framework for building 2d games, interactive books, demos and other graphical applications

A cross platform game engine that can be used to make simulations of any kind, ranging from simple prototypes to professional 2D and 3D games, simple physics or graphics demonstrations to robust, realistic simulations.

Free and opensource 2D+3D game making for indies

Limon is a multi platform 3D game engine mainly focusing on first person games. Focus of its development is ease of use and ease of study.

The successor version of Kirikiri 2, allows you to create 2D games and applications, and is used in many commercial adventure/novel games

Lightweight fantasy console for making retro inspired games

Dark Basic Pro is an open source BASIC programming language for creating Windows applications and games