Chaos
Simple rules, run a lot of times, until something appears that the rules never mentioned. Start one and leave it going.
21 of them
AttractorsTwo lines of arithmetic make a shape
ClothA hanging sheet in gravity and wind
Conway's LifeCells live or die by their neighbours
CosmosSix gravity systems, from sun to galaxies
DendriteFrost, coral and copper from one growth rule
DustColoured grains poured through heavy poles
ErosionRain cuts a heightmap into valleys
EvolveCreatures bred to cross five kinds of ground
Falling SandSand, water, fire and plants, poured in
FluidDrag ink through water
FractalsMandelbrot, Julia, Burning Ship and Tricorn
L-System GrowerRules that grow into ferns and dragon curves
LeniaCells hold shades, and creatures swim out
MurmurationThousands of birds, three rules each
Noise FieldAnimated fractal value noise
ParticlesThousands of particles under one force field
PendulumTwo or three rods on hinges
Reaction DiffusionCoral, spots and worms from two numbers
ResonanceTwo pendulums drawing over one another
SandpileGrains topple into a fractal
Slime MouldA million agents follow each other's trails