Is this openSUSE only, or can you build packages for other distributions with this service? It's hard to tell from their documentation or website.
EDIT: The openSUSE instance [0] says:
The openSUSE Build Service is the public instance of the
Open Build Service (OBS) used for development of the
openSUSE distribution and to offer packages from same
source for Fedora, Debian, Ubuntu, SUSE Linux Enterprise
and other distributions..
Can you actually build for Arch with this? I can't see an option for this, (thinking it might be a typo of yours). In addition, I'm trying to figure out how it works, what form do you need to upload the package as?
Yes you can. You just need a tarball and a PKGBUILD file. There's one downside in that in the official Arch repos, the sourcecode is just defined as a download link to the tarball but since the OBS builder can't access the internet (for security I guess) you have to provide a tarball yourself. The Build Service does however provide hooks for automatically downloading tarballs or grabbing code from version control systems.
EDIT: The openSUSE instance [0] says:
The openSUSE Build Service is the public instance of the Open Build Service (OBS) used for development of the openSUSE distribution and to offer packages from same source for Fedora, Debian, Ubuntu, SUSE Linux Enterprise and other distributions..
[0] - https://build.opensuse.org/
So it appears they do support different distributions, although I can't seem to find download links or examples.