AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.
T-Clock Redux - T-Clock Redux in an enhanced fork of Stoic Joker's T-Clock 2010 with ISO week number support...
Sleep as Android - Common alarm clocks ignore your sleep cycles, they wake you on schedule no matter your are currently in your deep sleep. Waking up from deep sleep is unpleasant, it makes you tired and it may negatively affect your productivity during the whole day.
ClocX - ClocX - freeware analog clock for Windows desktop with many features like calendar, alarms, skins, antialiasing and transparency.
Pillow for iOS - An iOS companion that helps you sleep better 💤