Ruby-Gnome Alerts allows one to set up alarms like an alarm clock.
With "Festival Tells Time", one can have the computer announce the time at regular times.
With "Popup Alert", one can have the computer announce a message and leave a popup with the message at regular times. This feature is useful for regular chores reminders, such as trash day, or billings day, etc... One can quickly set up a reminder for an recurring events, up to yearly events such as birthdays... One time events? Just delete the entry after it has run.
With "Open File", one can have the computer play a wav or mp3 file at regular times, such as a grand-father clock gong wav file... or a music mp3 file. If given a url like 'http://....', then a web-browser will open that page.
One can also add to the playable files and runnable applications by editing FILE_APP_MAP in the configuration file:
aplay plays wav.
xmms plays mp3.
timidity plays mid.
Lastly, one can run an arbitrary command.
Ruby-Gnome Alerts does not use the system's cron. The alerts will be active only as long as the application is running.