See end-nodes of dependency graphs

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http://unix.stackexchange.com – I'm using Arch Linux, with its Pacman package manager. I want to keep my system as clean as possible, and that includes not having any unused packages installed. But, because of dependencies, it's not a trivial task to have zero of such, at least with my level of knowledge. Is there any tool available, console or GUI, that will show me all installed packages that nothing depends on? (HowTos)