The rgeos package is an R wrapper for the GEOS library. GEOS is a powerful open source geometry engine written in C++ that implements spatial functions and operators from the OpenGIS Simple Features for SQL specification. rgeos makes these tools available within R and integrates with existing spatial data tools through the sp package.
This project is currently under active development; it has been released to CRAN, and may be downloaded within R using install.packages(), or from the package CRAN page.
The project summary page can be found here.