Home-Assistant.io - Home Assistant is an open-source home automation platform running on Python 3.
Alarmy - World's most annoying alarm app
ioBroker - flexible and modular application for the IoT and Smarthome
Galarm - Social alarm clock and reminders
openHAB - "empowering the smart home" - vendor and technology agnostic open source home automation
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.