Many distros have independent community generated package repositories though most aren't on official infrastructure. Ubuntu has PPA which is close. I try and avoid AUR as much as I can. It is a potential attack surface and packages are sometimes poorly maintained and break. I like it for system stuff and I mostly review the PKGBUILD. It seems like a good way for software to find a path into the official repos. There was a lot of resistance from me initially but for most desktop applications flatpak has proven to be a better solution.