Sometimes you want to see if a connection to a remote system is still alive or you just want to keep it alive by transmitting some data.
I've found the following little shell one-liner to be quite useful:
$ while true; do for i in '|' '/' '-' '\'; do echo -n $i; sleep 0.25; echo -ne '\b'; done; done
This will create a little ascii spinner and keep a line spinning until you press CTRL-C.