I created a very simple app this week using the Foursquare API. The purpose for building it is to understand the how to take in JSON data and use it with NodeJS. The app connects to the Foursquare API, and a For loop goes through my list of friends and pushes them into an array. The array is then rendered through ExpressJS, which dynamically displays it with Embedded JavaScript (EJS).
You can check out the web app here, and the Github repository here.
I also created an API for Cably, which accesses the database models in JSON format, and can be accessed here: Cably API