A clone of http://bitcoinmonitor.com using WebSockets instead of long polling and d3 instead of jQuery UI. The idea is to visualize all transactions in the global Bitcoin network. If you don't know what Bitcoin is, or don't know much about it, you should watch this two minute video.
The intention is to render trade data from all major exchanges as well as all account-to-account transfers and block creation events from the blockchain. The UI should eventually allow users to determine via a slider the date range they wish to see, hover for detailed transaction data, and ideally provide a Google-finance style set of checkboxes allowing the user to include/exclude which kinds of transactions they wish to see, which exchanges, etc.
A number of functionally equivalent implementations are available in the various sub-directories including Node.js, Node.js with SockJS, Tomcat-based Servlet, vert.x, and Atmosphere. See the README files in each for setup instructions.