Rule 110 (Wolfram, Cook 2004): Elementary 1D CA proven Turing-complete — the simplest known universal computer.
Rule encoding: 8 neighborhood patterns {111,110,101,100,011,010,001,000} → 8-bit output = rule number.
Gliders: Rule 110 supports stable, moving structures that interact. Cook proved universality by simulating cyclic tag systems with these gliders.
Class IV: Rule 110 is Wolfram's complexity class — neither simple nor fully chaotic. The edge of chaos.