John Graham-Cumming has released a cool new piece of open source security software called Shimmer. Shimmer provides an alternative to port knocking programs such as tumbler that are used to hide a valuable port (such as a hidden web server or SSH) on a public IP address.
Essentially shimmer works by changing a sets of ports (one of which forwards to the real service, and others that lead to a trap to blacklist attackers) on a timed basis. Legitimate users can determine the real port, avoiding the blacklist and getting a connection.
Shimmer Port Diagram
Credit: John Graham-Cumming