Etcha is a two-dimensional descendant of Jeffry Johnston's BitChanger. Like BitChanger, it has four instructions; unlike BitChanger, its storage model is based on turtle graphics, which permits it to be immediately used for an alternative purpose: graphical composition. Unlike the turtle in LOGO however, the turtle in Etcha is an integral part of the computation, playing a role similar to the tape head of a Turing machine.
Click "Start" to run the supplied example program. Or click "Edit" to modify it, and create your own program.