Yahoo purchased their "Open Sourced Traffic Server" a few years ago from Inktomi and has now released it to Apache because they think that it is a "great code". And it really is. It manages almost all of their Yahoo Mail traffic. They use it for edge processing and general edge caching, plus for the company´s load balancing. All pretty good stuff! The company calls it a "mature, reliable technological tool that supports half of Yahoo traffic". Everyone can use the app and modify and improve it... Pretty awsome, dude!