Please implement and integrate a GUI for port knocking. PK adds a simple but effective layer of security.
I imagine the PK GUI to be able to use/add/edit/delete a list of port knocking "sequences." Each sequence has one title, one host name, and then an arbitrarily-long, ordered list of port numbers and protocols (TCP or UDP). So, a sequence might be:
Title: The office LAN
#1: UDP 12898
#2: TCP 62181
#3: TCP 9999
You could also design the UI for the sequence as a string...e.g.
udp:12898 tcp:62181 tcp:9999
Several applications have integrated port knocking clients. For example, Enhanced TightVNC has it, and it will also be in an upcoming AlmostVPN (for Mac).