Gnome Clocks - Clock application designed for GNOME 3
ClocX - ClocX - freeware analog clock for Windows desktop with many features like calendar, alarms, skins, antialiasing and transparency.
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
LClock - Longhorn systray clock program
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
DS Clock - Keep your time synchronized with Atomic Time servers, using customizable digital desktop clock with westminster chimes.