Rails is a platform to serve your Ruby applications, and yet is a very well crafted open-source product written in the language that composes your apps. So, if you're curious to know how things work underneath your app, you can read everything!
This talk will be a good guide to step into the Rails internal. We'll cover these topics:
How Rails loads itself, libraries, and application when booting
How Rails deals with HTTP requests and databases
How to debug, patch, and extend Rails
Rails committer, Ruby committer, Haml committer, creator of widely used Rails plugins such as Kaminari, activedecorator, actionargs, html5validators, erd, databaserewinder, etc. Founder of "Asakusa.rb", the most active Ruby community in Japan.