pavbaranov [1] filed a deletion request for apper [2]:

It seems, that this application is abandoned even by upstream. We haven't got packagekit-qt4 (one of its dependency) even in AUR. So there is impossible to build it.

[1] https://aur.archlinux.org/account/pavbaranov/ [2] https://aur.archlinux.org/pkgbase/apper/