Right up my alley, Implementing with Sinatra and Datamapper
What you will learn from this book
* Discover in depth the major features of TinyURL, Twitter,
Flickr, and Facebook and what makes them work
* Discover how each of these popular Internet services can be
modeled with DataMapper
* Create clones of these Internet services using Rack and Sinatra
* Use third-party authentication providers with OpenID
* Deploy the cloned Internet services to the cloud using Heroku
* Use Amazon S3 to store data for your clones
http://www.amazon.com/Cloning-Internet-Applications-Chang-Sheong/dp/1849511063/