A package for thermodynamic modeling in geochemistry and biochemistry, with functions for equilibrium activity diagrams and chemical affinities of reactions, supported by an extensive thermodynamic database and group additivity for proteins.
The project summary page you can find here on R-Forge. (Development site, source code management)
Currently (Jan. 2013) the main website for the project is located at chnosz.net. (Downloads, help pages, output from examples and vignettes)
As a teaser, here's a random image from the examples of CHNOSZ 0.9-9, released on CRAN on 2013-01-01. Click here for a directory listing of all 54 images, or here for the images in context of the code running the examples.
Image filename: diagram9.png