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Nicky Case made The Evolution of Trust in 2017 as a free, open-source explorable explanation. It is built around the iterated prisoner's dilemma and draws on Robert Axelrod's tournaments, where simple strategies such as copycat performed surprisingly well.

Players test strategies against each other, then change the rules to see when trust grows or collapses. It takes about 30 minutes and has been translated into many languages by volunteers.

How to play The Evolution of Trust

The Evolution of Trust is played by working through short chapters. You first play a simple game against characters with different strategies, choosing whether to cooperate or cheat by putting a coin into a machine. Then you run tournaments to see which strategy earns the most over many rounds. Later chapters let you change the payoffs, the number of rounds, and how often mistakes happen, showing how each rule affects whether trust spreads. You only need a mouse or touchscreen.

1. Press Start and follow the chapters in order.
2. Choose to cooperate or cheat in each round of the coin game.
3. Watch the tournaments to see which strategies come out ahead.
4. Use the sandbox at the end to change the rules and run your own experiments.