Microsoft R OpenThis is the standard R version with the addition of the Intel MKL library for high performance linear algebra (including multi-threading).
Also included is a neat way to make sure your users use the same versions of packages as you did. This will make reproducibility easier. Basically the idea is to add a checkpoint command with the snapshot date in your script that verifies that the same snapshot is used by your users. They call this the CRAN Time Machine.
The microsoft site is called mran.microsoft.com (MRAN = Microsoft R Application Network). The icon seems to be a monkey with glasses:
Microsoft R ServerThis seems to be Linux only! I expected a Windows port.
It has some out-of-core and parallel algorithms for very large data sets, and some connectivity to big-data databases. Looks like you can get this with your MSDN subscription