Tool Name: fwknop - Firewall Knock Operator is a Single Packet Authorization implementation. The client allows you to sent authorization packets to a listening fwknopd server in order to open firewall ports.
URL: cipherdyne.org/fwknop
Source: cipherdyne.org/fwknop/download/fwknop-1.9.12.tar.gz

Why: More and more people are using fwknop to protect services on personal or work servers (eg. SSH, FTP, etc). For those of us who use BT, it would be useful to have this tool installed in order to open ports on our remote systems. BT does not have any other port knocking/SPA clients, however fwknop is probably the most used/actively developed/feature-rich implementation.

Feel free to contact myself or the author (Michael Rash) for questions/patches, as I'm involved with the fwknop project.