USE TURBO MODE! To change the rules, stop the project, click a rule to toggle it, and press the Random button to begin with a random input. If you change a rule, the project will start with a single on pixel at the top. Otherwise, it will continue with the last line of the previous run. After the project has appeared to stop, it will keep running to keep the rules invisible. You need to manually stop the project to change the rules.
My first project with a usable interface! :P Each line in this project is dependent on a set of rules applied to the previous line. Each rule determines the value of the pixel below any place where those three consecutive pixels appear. The lines are treated as a loop; the pixel to the right of the rightmost pixel is considered to be the leftmost pixel. If you turn on the first, last, and fifth rules, you've created a computer! See http://en.wikipedia.org/wiki/Elementary_cellular_automaton for more info, and to ruin the fun of experimentation. It's been over half a year since my last project, due to my work on a Java game. I probably won't leave Scratch any time soon, but projects will be less frequent.