Caffeine for Windows - Prevent your computer from going to sleep
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.
Caffeine for Linux - Inspired by the Mac OS X version, Caffeine for Linux is a status bar application able to...
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Caffeine for Mac - Caffeine is a tiny program that puts an icon in the right side of your menu bar.
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.