You can do a checkout from anonymous cvs at
cvs -d:pserver:anonymous@openacs.org:/cvsroot co openacs-4
which will give you everything or
cvs -d:pserver:anonymous@openacs.org:/cvsroot co acs-core
cd openacs-4/packages
cvs -d:pserver:anonymous@openacs.org:/cvsroot co calendar
to get the just the core and the calendar module.
the nightly tarballs are currently broken but
hopefully will be fixed soon. They are at
https://openacs.org/sdm/nightly-tarballs.tcl?package_id=9
