Hacktoberfest is a month-long celebration of open source software run by DigitalOcean in partnership with GitHub and Twilio.

The concept is quite simple, each person who creates five pull requests* on Github receives a T-Shirt and stickers.

This rather simple concept seduces a lot of people, here is the evolution of the number of participants:

* A pull request is a set of changes that are pushed to a repo.