I am involved in the development of the following R packages. The packages are available on CRAN (the Comprehensive R Archive Network). Some of the packages have their own homepage which may contain development versions and other resources.

R packages

gRain Homepage Graphical Independence Networks
gRim Homepage Graphical Interaction Models
gRbase Homepage Graphical modelling in R - base package
gRc Homepage Graphical Gaussian Models with Edge and Vertex Symmetries
pbkrtest Homepage Parametric bootstrap and Kenward Roger based methods for mixed model comparison
doBy Homepage Groupwise summary statistics, general linear contrasts, LSMEANS (least-squares-means), and other utilities
geepack Generalized Estimating Equation Package
Ryacas Homepage R interface to the yacas computer algebra system
See also: CRAN check results

Software not related to R

GUYacas is a graphical user interface (GUI) on Windows platforms to the Yacas computer algebra system.