[LAD] Harmonizer effects

[Phil Frost]

Lately I've been eyeballing some fancy $600 harmonizer rack units at
$music_store. (http://www.tc-helicon.com/VoiceWorks, for example) Not
wanting to drop that much cash, I got to looking for some software
effects that can do the same, without any luck.

Does anyone know if such a thing exists? Is it possible, or is it too
CPU intensive? If the latter is true, I was pondering some sort of FPGA
on PCI device for number crunching. I could think of a fun thing or two
to do with it. Has anyone ever done some similar work?