Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
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.
Online Alarm Kur - Free online alarm clock, set alarm easily on your computer using the internet alarm clock without downloading any software, wake up in time with the loud online alarm clock.
TIMEBOX - An advanced timer for professional meeting facilitators
KukuKlok - Kukuklok is a free alarm clock available online and offline.
Online-Clock.org - Online-Clock.org is an online digital clock to get your current local time and has options to set the alarm, stopwatch, and countdown.