Cron is a nifty way for Linux nerds to set up a command to be repeated over and over again. It’s time based so it’s really good for, say, backing stuff up at 2am every Wednesday.
The problem is, it’s so good I barely ever have to touch it; it just works in the background. This means I can never remember how to use it. Enter the cron calculator - you just dial in when and how often you want your task repeated, and it comes out with the correct expression.
This is more for my use than anything else, I can never seem to find it quickly when I Google it, and the others suck because they are poorly worded and hard to decipher.
Anyway, you can find it here.