Non-Linux FOSS: Persistence of Vision Raytracer (POV-Ray)
Back in the mid-1990s, a college friend (hi Russ!) and I would put our old 8088 computers to work rendering ray-traced images for days—literally. The end result would be, by today's standards, incredibly low resolution and not terribly interesting. Still, the thought of a computer system creating realistic photos from nothing more than math equations was fascinating. As you probably already guessed, Russ and I weren't terribly popular.