Piet program that prints "Hello World!".
Piet is an esoteric programming language designed by David Morgan-Mar, whose programs are bitmaps that look like abstract art.
I have written a brainfuck interpreter in Piet, a very fast Interpreter and a compiler that creates executable files from Piet programs.
Yusuke Endoh's program can compile an already existing brainfuck interpreter written in brainfuck into Piet. It has been written earlier than my brainfuck interpreter but I have found it after I wrote mine.
Allan Wirth's interpreter is more user-friendly than mine.
If you want to run very complex Piet programs like a Brainfuck interpreter executing 99 Bottles of Beer you should compile the Piet program with my PietCompiler to get acceptable execution speed. For smaller programs you may use npiet.