Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
Reminduck - A simple reminder app made for elementaryOS with Vala and GTK. - matfantinel/reminduck
Memo to Me - Online email & SMS reminder service.
Reminder Commander - Reminder manager that reminds you about important events in advance.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Digital Clock 4 - Beautiful customizable clock with plugins