Recently Amazon announced that they would be open sourcing the 3D engine and related behind their Amazon Lumberyard game tooling effort. As Lumberyard is based on CryEngine 3.8 (~2015 vintage), th… ...

However, that might change soon as Amazon is rebranding it and opening it up. Now called the Open 3D Engine, it's become an open-source project and part of the recently formed Open 3D Foundation.