While finite state machines and Petri nets sound too abstract or even out of place for web development, rest assured, they can be quite useful in your applications. If you have news articles that go from draft to review and then to published or webshop orders which are created, updated, and dispatched only to get returned and refunded, you might want to look into using state machines. Let’s learn one new pattern, see what popular libraries are out there, and how to use them to keep your business rules well organized and your concerns separated.