Tornado is an open source version of the scalable, non-blocking web server and
tools that power FriendFeed. The FriendFeed application is written using a web
framework that looks a bit like web.py or Google's webapp, but with additional
tools and optimizations to take advantage of the underlying non-blocking
infrastructure.

The framework is distinct from most mainstream web server frameworks (and
certainly most Python frameworks) because it is non-blocking and reasonably
fast. Because it is non-blocking and uses epoll or kqueue, it can handle
thousands of simultaneous standing connections, which means it is ideal for
real-time web services. We built the web server specifically to handle
FriendFeed's real-time features - every active user of FriendFeed maintains an
open connection to the FriendFeed servers.