Haiku Detector is a macOS app to find unintentional haiku in any text. Type or paste text into the Haiku Detector window and it will find any sentences or groups of sentences that can be split into lines with five, seven, and five syllables and display them in the lower part of the window. Then you can copy individual haiku, copy them all (Copy All Haiku in the Edit menu) or save them to a file (Save in the File menu.)
For now you can download it for free.
Haiku Detector makes no attempt to check for kigo (season words.) In a future version I intend to add some kind of learning algorithm so that Haiku Detector can work out which sound best as haiku, based on the word classes at the line breaks.
You can read more about the history of Haiku Detector, and some of the haiku found using it, on my Creative Output blog.