Unusual applications of regular expressions?
I don't know if this question belongs here (the answer could be subjective and depend on your definition of "unusual") but here is my favorite unusual application of regex:


  converting T9 input (2-9) to English text.


For example if the user wants to write hello they presses 42556. Convert the input to [ghi][def][jkl][jkl][mno] and test this regex against the whole vocabulary: the word hello will match.