Reminder Commander - Reminder manager that reminds you about important events in advance.
Reminduck - A simple reminder app made for elementaryOS with Vala and GTK. - matfantinel/reminduck
Memo to Me - Online email & SMS reminder service.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Digital Clock 4 - Beautiful customizable clock with plugins
Kana Reminder - Kana Reminder is a program which can be used to set a reminder to be triggered at a specified time.