Sweave (EssWeave) is a LiterateProgramming tool which is distributed with the R language (ArrLanguage). It is most widely used as a ReportGeneration? tool by academic statisticians preparing papers for publication.
See http://www.stat.uni-muenchen.de/~leisch/Sweave/ for information.
It is closely related to NoWeb, with some pretty-printing and plot-inclusion support specific to ArrLanguage.
KnitArr? (knitr; http://yihui.name/knitr/ ) is a cleaner reimplementation of Sweave, with LazyEvaluation (so that re-renders of a document that don't change the code don't force a lengthy recompute), and support for other document formats than TeX, like MarkDown and HTML.