Does anyone have any idea what tool / components are being used here?
It is the Control Knob. Found in Params > Input tab
Thanks for your response Michael - I actually meant the components off the screen that are causing the fillet?
I was understanding that filleting edges of solids was difficult in Grasshopper, and I desperately want to!
Ah, Grasshopper in Rhino 6 has new components for filleting edges of solids. They are not available in Rhino 5 Grasshopper.
But since that video is from 2014 I would guess that person made their own fillet component or definition.