I think regular expressions is something every programmer should be familiar with. I am not saying, every programmer should write three lines of regexp strings, in three seconds without a cheat sheet. I am just saying that we should all know at least that they exist and what they are useful for.
The truth is, if it is the first you encounter regular expressions, you might have some difficulty remembering all those hieroglyphic expressions. There are cheat sheets and they can be handy, but I found something today that in my opinion is quite better: Online Regular Expression Testing Tool
Do you know any similar offline/online tool?