Nebula is a program I wrote that randomly generates nebula-like procedural art. It's one of my most favorite projects to return to and tinker with.
I first started the project over the summer after my sophomore year of highschool. It was originally inspired by Mitchell Whitelaw's beautiful "scrunch / flower generator" on OpenProcessing.
Nebula uses the same mechanics as Curtain, except in 3D. It starts off with a randomly generated sheet of point masses, with each given a randomly directed force.
Over time, the point masses move along curves as this sheet swoops around. Each rendering is drawn with a low opacity contributing to the depthness of the structure.
You can try out Nebula, and see its source code, at OpenProcessing.