Released versions can be found at http://www.hylafax.org/download.html.
For invormation on obtaining CVS versions, see http://www.hylafax.org/cvs.html.
Released versions represent software that has been carefully tested on all supported platforms and is believed to compile, install, and function correctly (except where noted in the distribution documentation). Released versions take a long time to create and generally occur when the CVS version is stable and a worthy need arises.
CVS versions are test versions of the software that are distributed continually via CVS. These versions include new facilities and/or support for new systems. They are typically tested on one or two systems, but not always as thoroughly as released versions and not always on all supported systems.
See also here for how to identify which version of HylaFAX you have.