This is a module for php4 that I wrote a very long time ago that provides access to the rrdtool C library to php scripts.
The code is very old and buggy. It was picked up sometime around 2002 by a Debian project contributor and further development occurred within the Debian universe. You may be able to find the latest version of the code in the Debian repository, if they haven’t abandoned it yet.
I’m posting these files here for posterity and in case they may be useful to someone else.