http://www.apsis.ch/pound/

"The Pound program is a ReverseProxy, load balancer and HTTPS front-end for Web server(s). Pound was developed to enable distributing the load among several Web-servers and to allow for a convenient SSL wrapper for those Web servers that do not offer it natively. Pound is distributed under the GPL - no warranty, it's free to use, copy and give away."

Originally designed to work with ZopeApplicationServer