Apache Traffic Server
Apache Traffic Server is an open source extensible HTTP/1.1 compliant caching proxy server. Apache Traffic Server boasts caching capabilities that can improve response time while reducing server load and bandwidth needs by caching and reusing frequently requested web pages, images, and web service calls. It also offers "proxying" (see proxy server) to add keep-alive, filter or anonymize content requests, or add load balancing by adding a proxy layer.
The Apache Traffic Server was formerly a commercial product, however, Yahoo! donated it to the Apache Foundation, and it is now an Apache TLP (Top level project). The version 3.0.0 Apache Traffic Server release (June 2011) can handle more than 200,000 requests per second.