Horo - The best free timer app for Mac
Chronograph.io - Cloud synchronized stopwatches and timers.
Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Gestimer - For those little reminders during the day
(Not Boring) Timer - (Not Boring) Timer, a fascinating time tracking application that will let you stay on top of your task and remind you about the important events coming up on the same day.
E.ggtimer.com - A simple countdown timer with an alarm for the browser.