MarsSeed [1] filed a deletion request for sky [2]: Closed-source proprietary binary, "Lync and Skype for Business client on Linux". The company seems defunct, its website is "address not found". There does not seem to be a way to download this binary tarball anymore. But this package should not be needed. There are working alternatives for installing the official Microsoft instant messenger clients like Skype et al. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/sky/