> What I want is not just a GUI, but instead, one that displays *active 
> connections* as they appear and disappear, and allows changing rules
> on the fly. Is there such a thing? 

Have a look at conky. It has a.o. these output-possibilities:

Inbound: ${tcp_portmon 1 32767 count}  Outbound: ${tcp_portmon 32768
61000 count} ${alignr} ALL: ${tcp_portmon 1 65535 count}

Inbound Connection ${alignr} Local Service/Port

${tcp_portmon 1 32767 rhost 0} ${alignr} ${tcp_portmon 1 32767 lservice
0}

Outbound Connection ${alignr} Remote Service/Port

${tcp_portmon 32768 61000 rhost 0} ${alignr} ${tcp_portmon 32768 61000
rservice 0}

A thorough study of the documentation is necessary!

Peter.