Godot Engine 3 hit RC 1 today, and is now pretty stable. I've been having a fun time with it, and it supports a lot of features that closed source engines do. It's licensed under MIT.
https://www.youtube.com/watch?v=XptlVErsL-o for reference.
I was wondering if maybe Allegorithmic would consider making a Godot 3 plugin. One of the things that constantly bugs me is the lack of a Blender plugin. I understand why this is (because of GPL), but as Godot doesn't have any licensing restrictions I was thinking it would be a nice time for Substance to support an open source project.