building a visualization system for traceroute in the mid 90s was how i taught myself java.

traceroute itself was wrapped by a perl rpc wrapper and then a perl www cgi script would take a list of hosts and then reach out to all of them to ask them to traceroute each other, then a java applet would render an interactive graph that you could rearrange as you saw fit.

interesting learning: internet routing can be asymmetric!