I've had more than one post on this forum about plug-ins and techniques to do ADT (Automatic Double Tracking).
 
I just read a review of Waves Reel ADT and I watched the videos on the Waves website.  This seems to be a really good software recreation of the ADT created by Abbey Road while recording The Beatles.  The plug-in also has a few features that allow it to go a little beyond the original.
 
Oddly, however, the Waves videos call this effect "artificial double tracking."  I believe "automatic"—not "artificial" is the original term.
 
I plan to buy this.

Konrad,
 
I have the ADT from WAVES and am underwhelmed. Just my opinion though.
 
JK

konradh
Oddly, however, the Waves videos call this effect "artificial double tracking."  I believe "automatic"—not "artificial" is the original term.

 
I remember that it was first call "artificial double tracking". Apparently both names apply:
 
https://en.wikipedia.org/wiki/The_Beatles%27_recording_technology#Artificial_double_tracking 
 
https://en.wikipedia.org/wiki/Automatic_double_tracking
 

Hi, Konrad. I like Waves ADT. I've got their Doubler plugin as well and think ADT, especially when using the random LFO, sounds more natural. Also, it can be used for tape saturation. I don't have their J37 plugin, but I believe it's based on the same algorithm.

Hi, Konrad.
 
Have you tried ADT by Olaf Matthes?  It doesn't have much of a GUI, but it's free.
 
I used to use a couple of other free ones, but can't remember their names.  I'll have a look when I get time.
 
One was Duet by Martin Eastwood, I think.  Not sure if it is 64 bit, though.

Found this article in Sound On Sound, if you're interested.  Notice that it refers to "automatic double-tracking", also.
 
http://www.soundonsound.com/sos/apr09/articles/doubletracking.htm

I've never bumped into "automatic double tracking". IMO "artificial" is the correct option simply because it is artificial double tracking, not real double tracking.
The track is doubled automatically, but not double tracked. 

Thanks for all the replies and other options.