Gnome Clocks - Clock application designed for GNOME 3
Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
SleepBot - SleepBot is a sleep tracking app available in Google Play and the Apple App Store.
Digital Clock 4 - Beautiful customizable clock with plugins
Online Alarm Clock - The world's original online alarm clock, established in 2006.