TIMEBOX - An advanced timer for professional meeting facilitators
TimerLabs - TimerLabs is an interval timer that helps you with your daily routines and session based work
Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
HIIT (Watch) - A very simple interval timer engineered for Apple Watch
MetaClock.com - MetaClock is an Online Alarm Clock that can play YouTube videos and uploaded MP3s as an alarm tune. It supports Chromecast which means you can turn your TV or stereo system into an alarm clock. No installation is needed, it can also work offline.
Sportos - macOS interval timer that enhances your home workouts