fwknopclient is a graphical front-end to fwknop by Michael Rash written in Delphi.

fwknop implements an authorization scheme that requires only a single
encrypted packet to communicate various pieces of information including
desired access through an iptables policy and/or specific commands to execute
on the target system.  The main application of this program is to protect
services such as SSH with an additional layer of security in order to make the
exploitation of vulnerabilities (both 0-day and unpatched code) much more
difficult.