Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
Alarm Clock Pro - iTunes alarm clock, stop watch, timer, and more!
Gnome Clocks - Clock application designed for GNOME 3
KTimer - KTimer is a little tool to execute programs after some time.
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
Digital Clock 4 - Beautiful customizable clock with plugins