PassPort is a simple port forwarding utility. The program runs as an NT Service and can forward various ports from any of local interfaces to whatever remote IP address. It is easily manageable with a simple Windows GUI.
Runs on MS Windows XP or newer.
Did you check the "Code" tab here on SourceForge? That has the source.
The statement that this "Runs on MS Windows XP or newer" seems to be misleading, as I couldn't get this working in Windows 7. Maybe the problem was something specific to my setup, but I spent hours testing the ports being forwarded in all possible directions, and produced nothing.