Ray tracing is a computer graphics technique that produces realistic images of a three-dimensional scene. In 1987, Paul Heckbert (then at Pixar) announced a contest to produce a ray tracer in the minimum amount of code, as he describes in "A Minimal Ray Tracer." In 2009, Andrew Kensler (then at the University of Utah Scientific Computing and Imaging Institute) created a C++ version that can fit on a business card. Fabien Sanglard explicates this amazing piece of code in "Decyphering the Business Card Raytracer."
Zen photon garden is a 2D ray tracer in your browser. A blog post gives examples of what's possible and explains some of the unique details of its implementation.
The nightmare corpse-city of R'lyeh was built in measureless eons behind history by the vast, loathsome shapes that seeped down from the dark stars.
Have you ever wondered what non-euclidean geometry actually looks like? This video uses a custom ray tracer for the Minecraft engine to give some examples.
The Internet Ray Tracing Competition for November, December 2000. Some of these are amazing - and some only use POVRay for a renderer. Anyway, looks like Gilles Tran is probably going to win again. But who will take second and third? Props up to my good homey DSI for his phat submission!