Apple - Where is my crontab file?

In Mac OS X Lion the user crontabs are stored in /var/at/tabs. In the past they were located in /var/cron/tabs.

You should use crontab -e to interact with these in general, but knowing the location is useful for when you want to restore them from a backup of your disk, or something similar.

If you don't want to use launchd, you can edit your crontab as you would do on any unix systems :

crontab -e

Or, you can use a GUI software like CronniX.

The OS X way is to use launchctl to run jobs at a time.

For ease of use there are GUIs called Launch Control and Lingon.