fcron - Fcron is a scheduler designed for Unix/Linux systems, especially usefull when your system is not up all the day long.
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
Anacron - Anacron is a periodic command scheduler. It executes commands at intervals specified in days.
Gnome Clocks - Clock application designed for GNOME 3
mcron - mcron is GNU's implementation of cron. It is a 100% compatible replacement for Vixie cron.
AlarmDJ - Online Alarm Clock - Use YouTube videos or MP3 files as alarm sound. Works offline.