Boids
eater.net
Three rules are all a flock of birds needs
Sandboxes & Simulators
Two dozen physics scenes you can grab and throw about
brm.io
Instant · Best on desktop
Free, no sign-up · online since 2014
The demo gallery for a 2D physics engine, running everything from stacked boxes and chains to soft bodies, catapults, car suspension, gravity wells and Newton's cradle. Every scene is live and every object can be dragged, flung or dropped while the solver keeps up.
The soft-body and chain scenes catch people out, because you can pick up a wobbling blob and it deforms convincingly under its own weight.
Keep going
Picked for a shared category and overlapping vibe, not for popularity.
eater.net
Three rules are all a flock of birds needs
playgameoflife.com
Four rules, and cells that build spaceships anyway
pmneila.github.io
Two chemicals, two dials, and every pattern in nature
hunar4321.github.io
Coloured dots that attract and repel start forming cells
sandboxels.r74n.com
Falling sand with hundreds of elements and real chemistry
keiwan.itch.io
Build a jointed creature and let it learn to walk