Tornado is a framework developed at FriendFeed, a feed created with friends' news, articles, photos and videos and shared in multiple collaborative sites. With Tornado, users can access applications, websockets, and long polling code. This service is optimum for consumers who require lasting connections. The framework serves also as an asynchronous networking library.
In a world where real-time data streams are becoming much more common, and with the volume of that data continuing to increase, it makes sense that a framework would be developed to increase the ease at which that data can be processed. Yahoo! S4 isn't the first such framework to be concieved, or even open sourced, but it is likely to massively increase awareness that such frameworks exist, what problems they may help solve and get developers thinking about how they could use the technology and potentially increase the likelihood of somebody moving S4-like capabilities into the cloud and offering it as as service.