According to their tech talk about building it (http://www.slideshare.net/mongosf/real-time-ecommerce-analyt...), the original goal was to collect real time data to use in picking products for their gift page. I also heard that the other driving force behind building it was to have a visual way to show visitors to their office what Gilt's noon traffic spike really looks like/means. The core part is under the MIT license on github (https://github.com/mnutt/hummingbird) so it could easily be picked up by some of the other packages out there.