Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Simply Remind Me - Free email and text reminder service so you don't forget the important things in life!
Alinof Timer - Alinof Timer is a very easy to use timer for your Mac.
FollowUpThen - The simplest way to schedule an email reminder
CookTimer - CookTimer is a simple cross-platform countdown timer that helps when cooking, making tea or eggs.
Kana Reminder - Kana Reminder is a program which can be used to set a reminder to be triggered at a specified time.