Eye Rigger - Universal For Any Humanoid Model
The .zip doesn't install in Blender
Please un-zip the archive and open the .blend project.
Is this an addon (script)?
No, it's a plugin that uses a .blend file that has all the assets, textures and logic (node groups) inside for direct use. You can copy any of them over to any of your projects, while also preserving their original functionality. Before use, un-zip the archive.