Search for: nonfree/macros/latex/contrib/supported/rst
The package can also be downloaded (as a tar.gz file) from: http://www.reitter-it-media.de/software/rst-package.tar.gz
See http://www.reitter-it-media.de/compling/papers/reitter_rstpackage_2002.pdf for documentation.
"[The Package] is oriented towards the style of the diagrams shown in Mann & Thompson's Rhetorical Structure Theory and subsequent works. This package works perfectly with (LaTeX) and pdfLaTeX and does not require any special postscript capabilities in the output side."