Raspberry PI OS Builder

I had an Idea for a raspberry pi os builder, like there’s a gui, and the user drags and drops parts of a system to build an Operating System that can then be exported and run on a raspberry pi. Any Ideas how to do this or if it already exists.
I’ve already looked at this.

would this builder be a processing library? Or, one would use processing to build the GUI?

I am aware of this one: http://www.pibakery.org/

@dan850 It would be an app I write in processing.
@gohai I’ve seen that. What I want to do is create custom OS’s.