Anacron - Anacron is a periodic command scheduler. It executes commands at intervals specified in days.
fcron - Fcron is a scheduler designed for Unix/Linux systems, especially usefull when your system is not up all the day long.
Dead Man's Snitch - Monitor Cron Jobs and Windows Scheduled Tasks with ease.
entr - Run arbitrary commands when files change
VisualCron - VisualCron is an automation, integration and task scheduling tool for Windows.
Scheduled tasks - GNOME GUI for configuring a users' cron (automatic jobs). Some of its features are: