Pen Group is a project by a group of people who want to make advanced rendering more accessible and understandable.
Projects here are mainly written for the begginner's programming language Scratch!
Though some extend into GLSL and Javascript as well.
Pen Group was originally started to hold the Pen+ Shader Editor.
Scratch is simple, yet it allows for so much freedom on the users end. Pen Group seeks to bridge the gap between graphics APIs, like webgl, and the blocks of scratch.
Check out Pen Group's Github! There are a couple repositories there.