Kana Reminder - Kana Reminder is a program which can be used to set a reminder to be triggered at a specified time.
fcron - Fcron is a scheduler designed for Unix/Linux systems, especially usefull when your system is not up all the day long.
Desktop-Reminder - Desktop-Reminder is a freeware task planner for Windows to manage your tasks and other to-dos’ in really easy way.
Anacron - Anacron is a periodic command scheduler. It executes commands at intervals specified in days.
Memo to Me - Online email & SMS reminder service.
incron - This program is an "inotify cron" system. It consists of a daemon and a table manipulator.