Visual REGEXP ,by Laurent Riesterer , is a program that illustrates the mechanics of regular expressions, quickly build efficient regular expressions, etc. Currently at
My raving was deleted, but I reiterate it: never mind similar tools: this app can be improved, but it can't be beaten.
RLH: I use this app all the time. I have tweaked it (wider buttons and a quit button) but other than that I really like it.