This is my implementation of The Ray Tracer Challenge by Jamis Buck. From the website:
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! It’s easier than you think. In just a couple of weeks, build a ray tracer that renders beautiful scenes with shadows, reflections, brilliant refraction effects, and subjects composed of various graphics primitives: spheres, cubes, cylinders, triangles, and more. With each chapter, implement another piece of the puzzle and move the renderer that much further forward. Do all of this in whichever language and environment you prefer, and do it entirely test-first, so you know it’s correct. Recharge yourself with this project’s immense potential for personal exploration, experimentation, and discovery.
There is also a lot of helpful material on the official forums for the book, here.