Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
TIMEBOX - An advanced timer for professional meeting facilitators
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.
TimeMe - TimeMe is a multi-functional timer designed for sports training and workouts, cooking, school breaks, and coffee breaks.
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.