Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Fantastical 2 - Fantastical, the Mac calendar app you'll enjoy using. Quickly create new events with natural language input and more.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
Morgen.so - All-in-one Calendar, Tasks & Scheduler. Morgen is the single hub for everything that revolves around time management.