_why day commemorates the enigmatic disappearance of the influential developer and artist known as _why, who inspired many in the Ruby programming community with his creations, including the microframework Camping, the HTML parser Hpricot, and the UI Toolkit Shoes. To honor _why, a tutorial guides readers through creating a basic mailbox application using Shoes 4, a version now running on JRuby, which is a Ruby implementation on the Java Virtual Machine. The application interacts with the Nylas APIs to handle emails, allowing users to read, compose, reply, and delete messages, despite the inability to install the Nylas gem directly due to JRuby's constraints. The guide provides detailed instructions on setting up the necessary environment, including installing JRuby and additional gems like dotenv and httparty, and explains the application's workflow, such as utilizing the Nylas Messages and Send Endpoints for managing emails. Furthermore, the tutorial highlights the use of Regex for HTML sanitization within the application, discussing the challenges posed by Shoes' bundled Nokogiri version, and encourages readers to explore further resources to deepen their understanding of both Shoes and Nylas APIs.