<_description>
A sonar display pings (get it?) the hosts on your local network, and
plots their distance (response time) from you. The three rings
represent ping times of approximately 2.5, 70 and 2,000 milliseconds
respectively.
Alternately, it can run a simulation that doesn't involve hosts.
https://en.wikipedia.org/wiki/Ping#History
Written by Jamie Zawinski and Stephen Martin; 1998.