> Does akku.scm fit into your list?  I know it is a package manager, but does it have libraries it manages that are nowhere else?

Akku doesn't belong on this list as it's a package manager like
Snow-Fort. There almost certainly are some packages in Akku that have
not available from any other package manager, but neither Akku nor
Snow-Fort curates packages; they are publishing platforms where schemers
can send any package they like.

Some of the package collections on the list (at least slib, spells, and
wak) can be installed from Akku. I don't know whether those are
comprehensive or up to date, but they're listed on
<https://akkuscm.org/packages/>. Akku also mirrors all packages from
snow-fort.org.