Those of you who work with R (or Java) might be interested in FastR, an R virtual machine written in Java. You can find a full description in this PDF, but it looks like a useful tool for those using R, as it solves a number of common issues. R is not the fastest or most efficient language out there, and FastR aims to improve on it in a number of ways. The addition of a JIT compiler, for example, works to make R quicker.
According to the PDF, "R is legacy software that must be maintained, yet it must also evolve to meet new challenges." So, if you're interested in an R virtual machine written in Java to be faster than traditional implementations of R, take a look at FastR. You can learn more in the PDF overview, and check out these resources on GitHub as well.