This is a WWW interface for most of the EPICS CVS Repository. You can browse the file hierarchy by picking directories (which have slashes after them, e.g., src/). If you pick a file, you will see the revision history for that file. Selecting a revision number will download that revision of the file. There is a link at each revision to display diffs between that revision and the previous one, and a form at the bottom of the page that allows you to display diffs between arbitrary revisions.
The cvsweb script was written by Bill Fenner and improved by Henner Zeller, Henrik Nordström, and Ken Coar, then Akinori MUSHA brought it back to FreeBSD community and made further improvements; it is covered by The BSD Licence. The latest version of the script can be found at http://www.FreeBSD.org/projects/cvsweb.html