This page has links to older version of the code, some dating back to the early 1980's, and to development versions of the code, which may not be stable.
The current "gold" version is very well tested and stable. The link to that stable version is on the home page.
The current beta version is moderately well tested and the full test suite has been successfully run on all platforms. But it is still in the experimental stages. It is available here.
The previous beta, C96b4, is here.
Old versions of the code are accessed from this page. These are kept as a record of the results obtained by the code in the past. They are also an impressive demonstration of how much faster computers become every year. Each of these versions took about a minute to calculate a complete planetary nebula model when it was the stable version. (The current stable version does too). But on today's computers the older versions can do a calculation in surprisingly short times. The current version is not wasting time - it is just doing a far better representation of the physics.
The bleeding edge version is a very recent build that is in an undefined state. Physical processes may be disabled, spectacular bugs could be present, or massive amounts of print may be generated. It is available by ftp from here.