Goblin Engine is a custom build of Godot Engine 4.x created for personal use for my project. It provides additional functionality not officially supported. Please have a look at list of Goblin Changes to find out more. Goblin Engine is implemented as a Goblin module which does dynamic editor changes at runtime and action workflows which does additional changes to rename templates and executable and change icons.
Note that at this time Goblin Engine has no official releases since is very new. However the build system is used to produce release (GDScript only for now) Windows Editor build and release templates 64 bit only template file ready to be imported for Windows, Linux and macOS. See Goblin builds.
For additional builds you would need to either compile it yourself.
Discord server: https://discord.gg/erpDN9yUxN
Since Goblin Engine is compatible with latest 4.x Godot branch, you can find most the documentation you need over at Godot Docs.
The class reference is also accessible from the Goblin editor. Any new functionality is only documented in the built in Class references.