This document provides an overview of creating a mashup application using Node.js. It defines a mashup as a web page that aggregates data from multiple sources. It then discusses Node.js and how its asynchronous, non-blocking model makes it well-suited for data-intensive real-time applications. The document outlines sources of internal and external data that could be included in a mashup and recommends modules like Request and Async to simplify accessing these data sources from Node.js. It also provides tips on building the server, gathering and rendering data, and evolving the application.