I work for Spree Commerce, the most flexible eCommerce platform built with Ruby on Rails.
I'm writing an advanced book about Rails that costs only $15.00. Multitenancy with Rails teaches you how to build a multi-tenant application with Rails. Buy it now.
I wrote Rails 3 in Action, 1st Edition. There's a Second Edition coming, too.
For way too much more info about me: http://ryanbigg.com/about-me/