Have you ever wanted to force a script to act differently when it is invoked by cron? If the script is run interactively, for example, you might want the script to prompt the user for some information ...

Can I create a crontab file with vi without the crontab command? Currently working on a microcontroller linux distribution, and there's no crontab command, but cron exists... if only I could get a ...

Not a crontab solution but have a look at iCal alarms. I know they can be set to run when iCal isn't itself open but I don't know if they run when that user is not logged in.