Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
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.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
Sleepedy - Personal sleep coaching & therapy
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Pzizz - Sleep at the push of a button! Now with "Focus"