The blog post introduces HyperCard and Decker as platforms for creating interactive, multimedia documents, with HyperCard being a pioneering hypermedia system using the HyperTalk programming language since 1987, and Decker continuing its legacy with a similar aesthetic and functionality using the Lil programming language. The post guides readers through building a retro-style agenda application using Decker and the Ruby Nylas APIs, which involves fetching contacts from Nylas, processing profile images with MiniMagick and Lilt, and creating a .deck file that can be browsed in Decker. It provides detailed instructions on setting up the necessary Ruby environment, installing required software like Decker, MiniMagick, and Lilt, and coding the application to display contacts with their images in a pixelated format. The blog also encourages readers to explore more about Nylas's capabilities by visiting additional resources and joining a live stream for further learning.