Alarmy - World's most annoying alarm app
Fantastical 2 - Fantastical, the Mac calendar app you'll enjoy using. Quickly create new events with natural language input and more.
Galarm - Social alarm clock and reminders
Google Calendar - Spend less time managing your day & more time enjoying it
Alarm Clock Xtreme - Alarm Clock Xtreme: Alarm, Stopwatch, Timer (Free) is the most popular alarm clock app created and published by AVG Labs for both iOS and Android devices.
Itsycal - Itsycal for Mac. Itsycal is a tiny menu bar calendar. If you want, it will display your events as a companion to the Mac Calendar app. You can also create and delete (but not edit) events. Download Itsycal for macOS 10.