This project is where I refreshed my knowledge of Ruby on Rails.
I was following Michael Hartl's extremely useful guide on http://ruby.railstutorial.org/
I would highly recommend this guide to anyone who has an interest in learning RoR.

From his description:
The Ruby on Rails Tutorial helps you learn Rails by example through the development of a substantial sample application, 
including a site layout, a user data model, a full registration and authentication system, 
user-micropost associations, social "following", and a feed of status updates. 

The Ruby on Rails Tutorial also teaches good software development practices, 
including version control with Git and GitHub, test-driven development (TDD) with RSpec, 
and instant deployment with Heroku. 

Though of necessity the book and screencasts focus on a specific sample application, 
the emphasis throughout the Rails Tutorial is on general principles, 
so you will have a solid foundation no matter what kind of web application you want to build.