And for those of us with Linux (needs notification-daemon and libnotify):
#!/bin/sh
while true; do
sleep $((30*60))
notify-send -i applications-games -t 60000 "Play" \
"Hey, it's time to take a break\!"
sleep $((30*60))
notify-send -i applications-office -t 60000 "Work" \
"Now get back to work ..."
done