The Facebook Developer blog explains more about the framework, dubbed the Tornado Web Server. Written in Python, Tornado was developed from the ground up to handle thousands of simultaneous connections -- critical to powering FriendFeed's real-time functionality. Tornado puts its primary focus squarely on speed and handling the load from large amounts of traffic, differentiating it from similar frameworks in Python.
The Technology Behind Tornado
Facebook's Director of Products, Bret Taylor, explains on his blog the technical details of Tornado more in-depth. He also describes the backstory behind rolling their own web framework as opposed to simply using an existing popular framework like Django: "our performance and feature requirements consistently diverged from these mainstream frameworks."
In other words, if you're involved in a startup or company planning a product where real-time functionality will be critical, you now have another framework option to choose from that focuses specifically on speed and performance for real-time data throughput. Thanks to Facebook and FriendFeed, that framework is open source and free for your business to use and modify to taste.
For more information on the Tornado Web Server, you can check out its documentation, its source code, and join the developer mailing list.