Useful Ruby Methods For Sinatra (possibly, most likely, also for Rails)

After spending more time on a Sinatra project than humanly necessary, I came across a few Ruby methods I believe are very useful in creating an app that fulfills the basic requirements of CRUD (Create, Read, Update, and Delete), and then some. Some of these methods make it easier for the programmer to navigate through the multiple files and folders in a more seamless manner, and others allow for better user flow throughout the app in the browser.