Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
vClock - Web based time tools including Alarms, Timers, Stopwatch, and World Clocks. vClock is customizable and has a clean user interface.
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
YAPA-2 - YAPA-2 is a minimalistic desktop timer app for Pomodoro Technique users.
Gnome Clocks - Clock application designed for GNOME 3