Coffee was the primary tool I worked on during my stint at Groupon. It was an internal tool developed to help salespeople gain a competitive edge via exposing historical data on nearby merchants on a map.
It also included an interactive ROI calculator using websockets for real time visualizations of possible numbers to facilitate reaching an agreement between a merchant and a salesperson.
I initially prototyped a simple map-based interface exposing information from Groupon's data warehouse and Salesforce - effectively stitching the two together into one seamless interface. Although this used live data, it was limited and bare-bones. I used this prototype to do user testing along with our Product Manager to gather real user data about the desired functionality in the app, and what constituted acceptable real-world performance.
I then put together a small team of developers and settled on a Coffeescript / Backbone.js driven front-end app with a simple Rails shell underneath, hosted on Amazon EC2. We alternated cleaning up and making core functionality more sophisticated as well as ultimately building out entirely new features for different sets of users and use-cases. It was a great lesson in building a complex single-page, completely dynamic app.