Regexper – Regular expressions visualizer
It's always neat to see where one's ideas go!  AFAIK, I was the first person to create dynamic railroad diagrams for regular expressions (maybe 12 or 13 years ago).  I got the idea from json.org, which I think was Douglas Crockford's brainchild.<p>My initial implementation was strfriend.com (in Lisp: well under 1,000 lines, including views), and I think its main claim to fame was that Jeff Atwood made fun of it on Twitter.  (I was truly clueless at promoting myself back then.  Not only did I not have a Twitter account, but it didn't occur to me to submit it to HN.)<p>Every so often, I toy around with the idea of making it into a proper local/native application -- maybe someday.  In the meantime, my obsession with regular expressions lives on in my current application (see bio) where I parse and rewrite the user's entered regex syntax (ICU) into whatever regex syntax the backend requires.  I don't know of any other application that does this, but I predict that in 15 years it'll be commonplace (and I'll still be poor)!