Jolly at jollyrifficmods.com has one he's calling a Double-D-Cup. Its a bottom feeder that uses a 26650, not sure when he'll have them on the site, if he ever will. I built something similar myself a few months back. I also have home made a box
mod that uses two 26650's, its about the size of a dictionary.
But at the current moment, the only one on the market is the Helix.