BePresent - Duolingo for reducing screen time
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.
LeechBlock - LeechBlock is an extension for Firefox and Chrome that allows users to block time-wasting sites.
ScreenTime - Show your macOS desktop on FaceTime
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.