Airbnb’s engineering blog has a thorough posting about how Airbnb created its “Holiday Cards” application.  The objective of Airbnb Holiday Cards was to “let guests and hosts email greeting cards to one another, with custom art from our awesome designers and a personalized message from the sender about their experience.”  The challenges with the project were creating a positive user experience that also looked great on multiple screen sizes and integrated with Airbnb’s other services.  The blog post has details about how Airbnb transitioned from Ruby on Rails to Service-Oriented Architecture.  There’s also information about how Airbnb (YC W09) integrates technologies like nginx, ZooKeeper, Memcached, and Resque in a real-world production environment.