Godot is a fully featured, open source, MIT licensed, game engine. It focuses on having great tools, and a visual oriented workflow that can export to PC, Mobile and Web platforms with no hassle. The editor, language and APIs are feature rich, yet simple to learn, allowing you to become productive in a matter of hours.
Unreal Engine 4 is available to everyone. Epic’s goal is to put the engine within reach of everyone interested in building games and 3D content, from indies to large triple-A development teams, and Minecraft creators as well. For $19/month you can have access to everything, including the Unreal Editor in ready-to-run form, and the engine’s complete C++ source code hosted on GitHub for collaborative development.
Polycraft is a 3D action tower defence game.
Paintown is a 2d side scrolling beatem-up engine. Paintown supports game styles similar to the Sega Genesis game, Streets of Rage 2, as well as traditional 1 vs 1 fighting games through an implementation of MUGEN. Many aspects of Paintown are customizable, from the menu system to the levels and players that can be controlled. Paintown is highly portable. So far Paintown can run on Windows, OSX, Linux, BSD, Wii, PS3, Android and other systems.
OE-Cake! is a 2.5D fluids-based demonstration program for Prometech Software Inc’s Octave Engine. In the program, which acts as a physics-based paint program, users can insert objects and see them interact under the laws of physics.
Project Starborn is a building game like Minecraft with a very powerful engine behind it and advanced world editing tools. The entire world (and the game itself) is a giant sandbox that you can modify to your liking. If you want to create your own city, it’s as easy as placing a few buildings with a few clicks. You can also design your own buildings or games, giving you ultimate creative freedom!
2D game engine and level editor.
Frank Engine is an object oriented game development framework written in C++. The purpose is to be a fun and fast to create large open world 2D games. Everything necessary to create a fully featured game is included: physics (Box2D), rendering (DirectX), level editor, dynamic lighting, particle system, sound, music (Ogg Vorbis), gamepad input, GUI, and debug console. The code is fairly well documented and includes a simple starter project build on.