Probably better (for human creativity) if no one ever builds them, but surely I'm not the first to think of the following online prostheses for poetasters:
(1) A straight rhyme-grepper (words that rhyme with...)
(2) An alliteration-grepper (words that begin with...)
(3) Combining (1) and (2) with a thesaurus (grep only words that mean something like...)
(4) Metric constraints could easily be plugged in too
(5) And machine-aided metaphor
The reason it's probably better if would-be poets stay away from such devices is that necessity is the mother of invention, and the brain is such that once it senses that it can off-load a task onto another device, it no longer rises to the occasion. And then versification becomes just a multiple-choice exercise...