Anacron!

System Scheduler for Windows, Free Task Scheduling Software replace Microsoft Windows Task Scheduler

nnCron is an advanced and very powerful scheduler, scripting tool and automation manager. nnCron is very small in size (900k), but its capabilities are truly colossal. Besides possessing the traditional scheduler features (starting programs, displaying reminder messages and opening documents at specified time)

This program is an "inotify cron" system. It consists of a daemon and a table manipulator. You can use it a similar way as the regular cron. The difference is that the inotify cron handles filesystem events rather than time periods.

Fcron is a periodical command scheduler which aims at replacing Vixie Cron, so it implements most of its functionalities.

mcron is GNU's implementation of cron. It is a 100% compatible replacement for Vixie cron.