Someone needs to port a tiling window manager to iOS or Android. On a platform where screen space and user interactions are at a premium, it seems you'd want to minimize the amount of window resizing actions and maximize the usable screen space.
I use XMonad (http://xmonad.org/) on my desktop and love it. My Android tablet (a Nexus 10) is big enough that it needs something like this; would be great to have two or even three windows open at a time.