I was kind of curious about this too, as I would quite like to be able to do vocal effects in a similar vein to The Knife, Ellen Alien and Imogen Heap.
It does appear that there just isn't a plugin that tries to be a straight-up alternative to those TC Helicon and Digitech units. Harmony 4 appears to have been discontinued even.
So I think people just combine different pitch and FX plugins, because it's more versatile. Maybe try things like Ircam Trax and Soundtoys Crystallizer together?
Never heard about IRCAM TRAX, but I'll check it out thanks....
I don't know about Soundtoys Crystallizer but all the plugins that seem to be what I'm looking for (Antares Harmony, Eventide H3000 plugin and so on...) are quite pricey and requires iLok
I'm trying with the factory plugs in Logic and Ableton....but they're not yet what I really need