The link "OpenACS 5.1.0d2" from https://openacs.org/doc/openacs-HEAD/individual-programs.html#source-postgresql points me to https://openacs.org/projects/openacs/download/ but there is not tarball there.
http://cvs.openacs.org shows me old tags but no 5.1 tags
"openacs-5-1-0d2" tag is not recognized when using: cvs -z3 -d :pserver:mailto:anonymous@openacs.org:/cvsroot co -r o penacs-5-1-0d2 acs-core