Contrary to what the name of this installer originally suggested, it only contains the GUI from https://github.com/mabam/afpfs-ng-mac-GUI (my mistake when creating the installer). So you need both, this installer and the one from 9 Nov 2017.
Use this version with FUSE for macOS v3.x.
Use the version for 10.8 on Mountain Lion and up (tested on Mountain Lion and Sierra).
While testing the version for 10.6, on Snow Leopard the mount script hung. Might still work on other machines running Snow Leopard or Lion.
(I couldn't find the error, but Snow Leopard should be the last version of OS X that is still able to connect to MacOS 9 via AFP2.x without needing additional software).
After downloading, ctrl-click on it and choose 'open' (I'm not a paying Apple developer so the packages are not code signed).
Source for GUI v1.0 at https://github.com/mabam/afpfs-ng-mac-GUI/tree/ba96fbd205eefdd1ffd7df4b29263b759836ad08.