You start off with the same baseVM (I used to use Precise32, switched to Precise64 for the first time yesterday). You specify the boxes which is based off your

You start off with the same baseVM (I used to use Precise32, switched to Precise64 for the first time yesterday). You specify the boxes which is based off your base VM. From there, the path of evolution for each box will take place individually. If you have a Vagrantfile that specify for one project to use Ruby2.0beta and another Vagrantfile for another project to use Ruby1.9, you essentially have two boxes, two execution environments, but you still code on the same machine.