The xo-4 Touch can do it. You simply launch two windows each with a book, and slide around and resize the windows.
If you need to do that often, you could try to install Compiz on top of the existing gnome 2, so you could simply hit Windows-right arrow for one window and Windows-left arrow for the other window. That will automatically give you a left and right tiling without needing to resize manually. Then you hit control-rt arrow in both windows to rotate 90 degrees, then you effectively have a top and bottom split with just a few key presses.
Note the discussion here if you actually want to acquire one:
https://www.mobileread.com/forums/sho...=265318&page=3
In short, you can't simply buy one of these on amazon.com.