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.

ActivityWatch - Log what you do on your computer. Simple (yet powerful), extensible, no third parties.

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

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.

Time Doctor - Time Tracking and Time Management Software that is accurate and helps you to get a lot more done each day.

Cattr - Cattr is a free open-source self-hosted time tracker with desktop clients for windows, mac, linux.