For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:GNUstep/openSUSE_Tumbleweed/X11:GNUstep.repo
zypper refresh
zypper install gnustep-base
For openSUSE Factory PowerPC run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:GNUstep/openSUSE_Factory_PowerPC/X11:GNUstep.repo
zypper refresh
zypper install gnustep-base
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:GNUstep/15.6/X11:GNUstep.repo
zypper refresh
zypper install gnustep-base
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:GNUstep/15.4/X11:GNUstep.repo
zypper refresh
zypper install gnustep-base