I've seen this utility in use, so I know it exists. I've scoured Google for an hour but can't turn up anything besides hosts3d, which isn't it.
This utility would run on a firewall box (or in-line with a gateway). It shows graphically packets being dropped and allowed. The packets would fly in on one side of the screen and bounce back if rejected, but pass to the other side if allowed. I remember it made me think of pong.
Anyone know what I'm talking about?