The MongoDB Atlas Hackathon is a 30-day challenge that encourages developers to showcase their creativity and skills by building projects using MongoDB. The hackathon runs from December 13th to January 13th, with five grand prize winners each receiving $1500. To participate, developers must submit a published post on DEV using the #atlashackathon tag and have a public GitHub repository with an Apache 2 license. The project can be solo or collaborative, and there are no specific rules other than utilizing MongoDB. The hackathon aims to foster creativity, innovation, and fun among developers, with prizes and recognition for outstanding projects.