In the last post, I outlined a simple way to adding to the Ruby.framework bundle the newer version of the Ruby Language, 1.9.
Well, as I finished that up, I started hacking around with some other code, and a friend was trying to show me something neat with Ruby-HEAD... Well, that made it difficult to add a HEAD into the bundle, since the bundle is supposed to be pretty static and not prone to constant modifications. My way works for simple things (get 1.9, end).
He suggested I try RVM. Ruby Version Manager is a simple little script that will download, configure, make and install specific versions, as well as patchlevels of the Ruby language into your $HOME directory.
I havent delved into exactly how it works, but it looks like it dynamically updates your path to the bin directory of the versions installed into your $HOME. So even when you install a gem (say, mongrel) that installs an executable, it will run as the default version.
You can also install specific "GemSets", which is a fancy way of saying... set of gems.
I highly suggest everyone who uses Ruby to take a look at it.