Tonight I was randomly wandering around online when I bumped into something quite peculiar: Piet. It's a programming language named after Piet Mondriaan, the Dutch abstract art-ist. In this programming language, a program is actually an image where each color determines what to do. The color decided where the instruction pointer will go next, what to do with the stack and what to output to the user. It doesn't serve much of a purpose, but it's one of the most interesting esoteric programming languages I've encountered. One program in particular made me smile, which I can link here as a bitmap.
Besides being a picture of a circle, this is also a Piet program that calculates the number pi. The best part is: if you increase the image size, the approximation of pi becomes more accurate. Brilliant!