I'm with new project named Coarse Port Knocking.
This is a simple implementation of Port Knocking techniques.
This sniffs network packets with determined keys and executes commands like firewall to open and close ports. In the client mode injects packets with key to server.
This is a personal project of the your author and is available for everybody by your GPL Licence.
More information:
http://coarseknocking.sourceforge.net/