That reminds me of Chaotic AUR, though it’s an online public repo. It automatically builds popular AUR packages and lets you download the binaries.

It sometimes builds against outdated libraries/dependencies though, so for pre-release software I’ve sometimes had to download and compile it locally still. Also you can’t make any patches or move to an old commit, like you can with normal AUR packages.

I’ve found it’s better to use Arch Linux’s official packages when I can, though, since they always publish binaries built with the same latest-release dependencies. I haven’t had dependency version issues with that, as long as I’ve avoided partial upgrades.