From Coral Works:
WebDelegator is a server solution that permits a collection of Web servers to be hosted on a single IP address. The software accepts connections on a particular address, and establishes connections to the appropriate Web server to fulfill the requests. The HTTP request header is used to determine the destination Web server, and to preserve the IP address of the originator.
Administrative Web interface allows the monitoring of connection and data transfer statistics. Access control lists allow the filtering of incoming connections. Optionally integrates with Internet Information Services (IIS) for its advanced abilities.