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.

Kapow - Kapow is a punch clock program designed to easily keep track of your hours, whether you're...

RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.

Kimai - Kimai is a free open source timetracker.

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.

Personal Task Manager - PTM is an Open Source time tracking tool hosted by Sourceforge.net.