A food-ordering app for customers and kitchen staff: limited daily dishes, live order tracking, and a kitchen board that updates the moment a payment clears. The hard part is staying correct when many people act at once — limited stock is never oversold, a retried checkout never creates a second order, a duplicated payment webhook never charges twice, and every cent moves through a double-entry ledger. Each of those guarantees has an integration test against a real PostgreSQL database.

Spring Boot 3 (Java 21), React, PostgreSQL. The restaurants are fictional and payments go through a simulated card processor.

Code: github.com/Rolinmuuu/Online-Order