Not sure if I called it the right thing. The question on Double Knitting reminded me about this. I'm not asking about Tunisian/Afghan/Cro-knit . . . . this is a crochet hook with a crochet hook at both ends, I'm pretty sure. I think.
I have a booklet published by Needlecraft Shop called Dishcloths on the Double using a technique called "crochet on the double". I think this is what you're talking about. Don't remember for sure, but I think I got the booklet from Annie's Attic. The first page demonstrates the basic technique then each pattern practices something different.