If you are referring to
https://openacs.org/projects/openacs/download/then you probably want 5.1.5 core, which is the most recent stable release. Since it's written in a script language, OpenACS does not have a source vs non-source distinction; the final product is the source.
There is no tarball containing all of the packages; you can either download the core tarball, install it, and get the other packages from the repository via the Admin functionality, or get everything from cvs. To do that, see
https://openacs.org/doc/current/using-cvs-with-openacs.html