The document discusses Google App Engine and options for building applications on it using Ruby and a new language called Duby. It provides an overview of App Engine architecture and billing models. It then covers using Ruby with App Engine via JRuby, frameworks like Rack and Sinatra, and the DataMapper ORM. Duby is introduced as a statically-typed language inspired by Ruby syntax that compiles to Java bytecode for the App Engine environment. Examples show a simple blog application built in both Ruby and Duby styles.