Crontab UI - Easy and safe way to manage your crontab file
Desktop-Reminder - Desktop-Reminder is a freeware task planner for Windows to manage your tasks and other to-dos’ in really easy way.
Scheduled tasks - GNOME GUI for configuring a users' cron (automatic jobs). Some of its features are:
Reminduck - A simple reminder app made for elementaryOS with Vala and GTK. - matfantinel/reminduck
024h Lucky Reminder - 024h Lucky Reminder is a reminder software for home and office.
Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS