HAProxy

HAproxy, is a GPLv2 tcp and http proxy server software written in C. It's used by some big sites. Conveniently, if you need a reverse proxy, you should also be able to use a load balancer, and balance whenever you want as well.

Reverse Proxy

Here some samples of folks using HAproxy as a reverse proxy:

Docker

Reverse Proxy for Docker (ooo new hotness) http://oskarhane.com/haproxy-as-a-static-reverse-proxy-for-docker-containers/

IPv6

It is also possible to use HAProxy as a reverse proxy for IPv6 clients as a buffer with IPv4 services (e.g. a webserver):