Gnome Clocks - Clock application designed for GNOME 3
Clock + - Alarm clock, timer, and stopwatch application for Android
Digital Clock 4 - Beautiful customizable clock with plugins
Clock Tab - Clock tab allows you to view the time right in your web browser!
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
Sveglia - A free alarm clock that can sound an alarm, execute a program, or shut the system down.