Pester - Pester: simple, disposable alarms and timers for macOS
Digital Clock 4 - Beautiful customizable clock with plugins
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.
Gnome Clocks - Clock application designed for GNOME 3
Task Scheduler - The Task Scheduler enables you to automatically perform routine tasks on a chosen computer. Task Scheduler does this by monitoring whatever criteria you choose (referred to as triggers) and then executing the tasks when their criteria are met.
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.