The Comprehensive R Archive Network (CRAN), maintained by the R Project, is updated frequently with new R packages & R releases at cran.r-project.org. Use the Time Machine to browse daily CRAN snapshots as far back as Sept. 17, 2014. These snapshots provide reproducibility for Microsoft R Open (and older Revolution R Open) releases and the checkpoint package.

See another snapshot:  

Now viewing CRAN snapshot from: