virtualbox
Vagrant offers an unprecedented level of ease when it comes to recreating the same development environment across different machines. I currently am stuck with windows as my main OS, both at home and at work. Most of the work I do at home revolves around Node.js (and currently a bit of ruby too, thanks to Jekyll, but that might be changing soon) whereas the work that I do at the office mostly involves C++ and cross-compilation to QNX.