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.

See also:

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.