Hourglass - Hourglass is the most advanced simple countdown timer for Windows.

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.

Alarm Clock Tab - Web based time tools including alarms, timers, stopwatch, and time zone converter. Resources also include Tabata, Pomodoro and other useful tips and tactics for managing time and time tracking.

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.

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