I like the R Project for Statistical Computing to which I contributed three packages:

BayHaz R Functions for Bayesian Hazard Rate Estimation
FBFsearch Algorithm for searching the space of Gaussian DAG models through moment fractional Bayes factors (joint with D. Altomare and G. Consonni)
giRaph The giRaph package for graph representation in R (joint with J.H. Badsberg and C. Dethlefsen)

I have also developed some R scripts for Bayesian inference, first coded on the occasion of ABS07: Summer School on Bayesian Methods and Econometrics.

"Il semble que la perfection soit atteinte
non quand il n'y a plus rien ajouter,
mais quand il n'y a plus rien retrancher"