I don't know if the project is still alive, but the code they've released is a functional reference implementation. Another approach is to adopt Google's ICE implementation which is used in Google Talk and realease under a BSD license as part of libjingle. Google accomplishes NAT traversal using a reliable UDP stream in tandem with a standard STUN server; this avoids the complexity associated with TCP hole punching. Yet another place to look for example code is in open source P2P projects, which often implement NAT traversal using either STUN or STUNT (Jive Software's OpenFire is just one example).Here's a great document on NAT traversal: http://www.brynosaurus.com/pub/net/p2pnat/
Google's libjingle: http://code.google.com/apis/talk/libjingle/index.html
Now, if you were to establish a source licensing model *hint, hint* I could write the STUNT code and donate it back to s-code... of course, for a nice discount on the license. 