This one comes care of /r/gamedev and I have to say on first glance I am rather impressed. This is a C++ based open sourced game engine with a WYSIWYG editor and C# scripting support. A look at this screenshot from the Github page should get you somewhat excited:
The engine description direct from the author:
A modern open-source game development toolkit. It aims to provide simple yet powerful environment for creating games and other graphical applications. A wide range of features are available, ranging from a math and utility library, to DirectX 11 and OpenGL render systems all the way to asset processing, fully featured editor and C# scripting.
For game developers Banshee aims to provide a complete set of tools and APIs needed to make a game from start to finish. It provides a highly intuitive and customizable editor that is easy to use by artists, designers and programmers alike, supporting development stages from asset management, scene building, scripting to game publishing. C# scripting makes your development easier by giving you access to the entire .NET library, along with fast iterations times while being safe and easy to write. Editor is fully extensible with the help of specially developed scripting API so you may customize it for exact needs of your project.
For engine developers it aims to provide a high quality foundation to build and improve upon. Banshee runs on a powerful multi-threaded C++14 core created to take advantage of all resources modern hardware can offer. Built from ground up using modern design principles, everything is modular, layered and decoupled as much as possible, making it easier to modify, replace or add functionality. Platform specific functionality is kept at a minimum making porting as easy as possible. Additionally every non-trivial method, class and field is documented. All this combined makes Banshee a great platform to build upon, for developing higher level systems like editor tools, core enhancements like new rendering techniques and platform ports, all the way to creating fully specialized toolsets that fit your team's needs exactly.
Engine code looks nice and clean from the examples shown:
renderWindowDesc.videoMode = VideoMode(1280, 720);
renderWindowDesc.title = "My App";
renderWindowDesc.fullscreen = false;
The engine is currently Windows only and requires Visual Studio 2013 or 2015. I have to say by first impressions, this is certainly an interesting looking engine and one I will have to check into a bit closer if I get the chance. Obviously it’s a 0.2 release, so expect the usual menagerie of bugs and performance issues.
If you are interested in learning more, be sure to check out the introduction video: