Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.
Timer Tab - Online countdown timer, alarm clock, and stopwatch.
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.
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.
Clockify - Simple and free time tracker. Perfect for small and mid-sized businesses as well as freelancers. Unlimited projects and users, unlimited productivity. Get all the premium functionalities, completely free.
Online Stopwatch - Online Stopwatch is free to use online tool that allows you to keep track of the important events and tasks that you are performing.