The Concurrent Version System (CVS) maintained by Cyclic Software was selected for use by the OpenBSD project group. With CVS, seventy or so developers are able to update the source code (which is over 1349 MB, around 75000 files) that comprise the OS, ports/packages, and XFree86. A large number of OpenBSD users can download the OS sources via anonymous CVS, a procedure that is much more reliable than the Software Upgrade Protocol (sup).
CVS also allows easy creation and maintanance of branches so that we can provide a release + patches source tree and a up to the minute development source tree with parallel development.
Since CVS interfaces with the Secure SHell (ssh) it can provide reliable user and host authentication. This fits in well with the OpenBSD project's goal of security.