Is there any lightweight appdriven window manager?

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http://askubuntu.com – I've recently installed lubuntu on my cubbietruck board and it's great in terms of ressource usage, but i'm just addicted now to a UX where you switch between apps, not windows. Like on MacOSX or normal Ubuntu Unity, when you switch between Tasks wih Alt + Tab, you switch between apps and then between windows and there is also no window preview for every opened window on your dock, but only for the opened apps. Is there any lightweight window manager with that application driven paradigm and not that document oriented paradigm from the 90's? Or would just installing Cairo Dock with xcompmgr d (HowTos)