PortReflector for Mac

From Wickedly Simple Software:

PortReflector allows a Classic application to access the Internet via Mac OS X's PPP connection. PortReflector works by reflecting inbound TCP/IP ports to computers on the Internet. Each port mapping needs to be configured (the first time), making this solution workable for applications that connect to a known server (such as mail, news, or Telnet). This solution will not work well for programs such as Web browsers, since they hit too many different servers. The solution will require a one-time change to a Classic program's configuration. Setup instructions are included for Outlook Express, but can be easily adapted for use with other programs. PortReflector is also designed to accept TCP connections on a configured port and reflect them to another host or port number.