RVM http://rvm.beginrescueend.com/ is a great tool to run multiple isolated Rubies on your machine. I personally use it to manage my CRubies and various gemsets. However, last night I had some problems due to the way rvm works and the way I was using it so I figured I should share it with the list. I don't use rvm for MacRuby, I use the nightly builds or compile from source. Last night I was debugging Rubygems and noticed something really weird about the gems Rubygems thought it had installed. Turned out that I had set my terminal tab to use rvm with Ruby 1.9.2. Rvm automatically changes the gem path environment variable and even though I was using macgem, rvm hack was affecting my macruby setup. I had to switch back to the default Ruby ($ rvm use system) o go back to the normal behavior and get macgem to see the proper macruby gem path. This is really a small thing since hopefully you don't have rvm set with a default ruby than the system's and that you open new terminal tabs to run MacRuby scripts. Still, it's good to know about this behavior in case you encounter the same weird behavior I did last night. - Matt