Three-Four days ago I was in a situation where I need to have multiple versions of ruby and rubygems on my ubuntu machine. I was lucky, I found an awesome article http://blog.michaelgreenly.com/2008/08/multiple-versions-of-ruby-on-ubuntu-2.html. This really solved my problem, Many thanks to Michael Greenly.
If you ask me I would say best way to manage multiple versions of ruby in any platform is RVM. It is really easy way to manage multiple versions with RVM and porting the existing gems which is the biggest headache http://rvm.beginrescueend.com/examples/
Looking around
I like to look around the online world, regularly I will just go to Digg and follow thru