Timer Tab - Online countdown timer, alarm clock, and stopwatch.
Amazing Marvin - Customizable personal productivity tool
Online timer - Online timer is a free and easy-to-use tool that comes with a very simple way to get done with measuring time and alarm.
Focusmate - Distraction-free productivity via virtual coworking
Gestimer - For those little reminders during the day
MenuTimer - MenuTimer is a timer that you can use from your menu bar.