This is my first semi-useful Flash application.
It strives to visualize the output from "netstat -np tcp" (active TCP connections) in a pretty and yet informative manner.
The program maps each IP-address to a point in 3 dimensional space, skewing space to put your server in the middle and then drawing colored lines to each connected host from there. Space rotates slowly and the list of points is peridically refreshed with new data from the server. If you mouse over the ends of the lines, you can see exactly which IP addresses are involved.
The mapping is designed to group "similar" IP addresses together, giving visual clues on whether clusters of machines (such as search-engine spiders) are actively connecting to your server.
Currently, this will probably drive your flash player nuts on a very busy (or under attack) server.
To enable Crystat on your own server, simply copy the crystat.cgi and crystat.swf files to a folder on your web server. Then configure the web server to allow crystat.cgi to run as a CGI program, and point your browser at the .swf file. That should get you up and running.
You may subsequently want to edit crystat.cgi to disable some of the privacy options to make the tool more useful - however, if you do, please consider password-protecting access to Crystat as it may reveal information of potential interest to hackers.