It is open source alternative to Unity3D and UnrealEngine that bundles 3D engine, scene editor, code editor and debugger. The editor is much more lightweight and faster than competition so you can use it even on older laptops. Supported languages are GDScript (python-like), C# and visual programming with routing nodes. There is also support for native code execution which allows community to hook up their own favorite language.
The engine targets all major platforms including mobile and VR. Consoles are not supported due to necessary NDAs, but there are still some Godot games deployed.
Some things lack polish (API documentation mostly), but the development and community around it is very active and positive. Works best with Blender as modeler. Currently the Vulkan support is in works and planned for next major version.
Its current big downside (which I hope they address in an upcoming version) is that it lacks occlusion culling. So while it does have half decent VR support, for example, the performance in anything but very simple scenes is quite poor.
[1] https://godotengine.org/