Hacktoberfest is a five-year-old program that aims to give back to the open source community by encouraging developers to contribute meaningfully to projects and earn limited edition t-shirts. The event, now in partnership with GitHub and Twilio, has seen over 100,000 developers from 120 countries participate, contributing nearly 400,000 pull requests to almost 100,000 repositories. This year's celebration will have new rules and details, including a cap on t-shirts, more resources for beginners, and the introduction of "Hacktoberfest Values" to bring participants closer together around the shared goal of giving back meaningfully. To participate, developers must make five pull requests between October 1-31 in any timezone to any public repo on GitHub, with the first 50,000 participants earning a shirt. The program has led to significant offline community growth and connections among developers, with companies like SendGrid and OpenEBS dedicating their teams' time to participating.