This document discusses the evolution of bootstrapping Rails applications from the initial Rails generation to modular templates called App Lego. It outlines how initial Rails apps took a lot of time to set up, then skeletons and templates sped things up but lacked modularity. App Lego used templates in a modular way, allowing developers to choose which features or modules to include. Each module is its own template that can be included. The document acknowledges some downsides like long command lines but outlines future plans to improve the user experience.