Vivarium

Dozens of creatures drift through a dark pond. Each carries a small neural network that senses nearby food and neighbours and decides how to move. Nothing tells them how to feed. The ones whose brains happen to steer them toward food live long enough to reproduce, and pass on a slightly mutated copy. Watch for a minute and a sparse, starving pond turns into a crowded one.

Sometimes it goes further. A lineage stops grazing and starts hunting the others, and a predator–prey arms race begins that nobody wrote. A live phylogeny below the pond tracks species branching, sweeping, and going extinct in real time. Seasons and biomes mean when and where a creature is born both matter.

No build step, no dependencies, no install — it opens in a browser and runs. The repo is named claude_imagine because that is where it started.