The new Facebook app seem to have done away with the grid-icon layout, with a more interesting custom navigation layout where the bottom-most view shows all the options (like Profile, News Feed, Messages etc for Facebook) and clicking on one of them brings another view sliding over the top. You can press the 3-lines button to then expose the bottom-view again, but the current view is partially visible. The Path app also recently updated to match this scheme.
What's the best way to recreate this? I've searched for any open-source options but haven't found them. Three20 doesn't seem to support this either.