#100DaysOfGatsby is a guided coding challenge organized by Gatsby for 2021, aimed at helping developers, like the fictional character "Dev," to build a proof-of-concept website for the startup AudioC0RE using Gatsby. The challenge is structured with various phases, including community support on GitHub and a coding livestream, offering participants the opportunity to learn best practices. Dev's task involves creating a simple Gatsby site connected to Contentful, employing Gatsby's routing API and incremental builds on Gatsby Cloud, with the focus on functionality rather than content or styling. The initiative highlights Gatsby's suitability for handling traffic spikes and its extensive plugin ecosystem, providing resources for developers to familiarize themselves with Gatsby and related technologies. Participants are encouraged to seek help from the Gatsby community for any questions, as the internal team emphasizes independence to maintain productivity.