Mobile devices are designed primarily as a modal experience. You use one app at a time, but can switch between them quickly. Multi-window interfaces and floating apps have been implemented a few times as an alternative, but most of these solutions are a bit clunky. Ixonos has released a new video demo of its multi-window technology, and it looks much better. If only we knew where to get it.
This is very awesome, and essentially very similar to Metro snapping - except with traditional windowing abilities, something Metro should have as well. They won't say who they are developing this for, but I wouldn't be surprised to eventually see Android applications running in a similar fashion on ChromeOS.