Turnstyle is a graphical esoteric programming language loosely inspired by Piet. Both encode programs as images, however, the similarities end at the syntax level. Where Piet is really a stack machine in disguise, Turnstyle is an encoding of the (untyped) Lambda calculus. This allows for building more reusable images at a higher level of abstraction, while still keeping the specification small, making it relatively easy to develop new interpreters.

I just got the examples running. Very cool! (Earlier I was trying to run the images on the page in the playground, but I needed to run the links on the images.)