Here are some Demonstrations that are relevant to Chapter 3 of A New Kind of Science. They are grouped under relevant section. Haven’t read Chapter 3 of NKS? Start reading here
More Cellular Automata
Cellular Automaton Explorer, by Stephen Wolfram – Cellular automata are a central example of Stephen Wolfram’s science, and of simple programs in the computational universe. Explore some of their amazingly rich and varied behavior here. See Wolfram’s rule 30, and then choose more colors to explore rules that have probably never been seen before.
Examples of 1D Three-Color Totalistic Cellular Automata, by Abby Nussey -This Demonstration lets readers of A New Kind of Science explore one-dimensional three-color totalistic cellular automata as given in the examples on pages 62–64, and 66–70.
Mobile Automata
3-Color Left/Right Mobile Automata, by Narine Manukyan -This Demonstration shows the behavior of a mobile automaton with two states and three colors. There are 
rules, but this Demonstration shows only rules from 677,855 to 780,055.
Register Machines
Register Machines, by Anthony I. Joseph -(excerpt): This Demonstration allows an exploration of the register machines discussed in chapter 3 of A New Kind of Science. Register machines are treated as logical abstractions of physical registers used in electronic devices. Registers are often used to store information to be used for storing data and performing calculations.
