RVM or Ruby Version Manager allows you to run multiple instances of Ruby within your user space. No need for root or admin privileges with RVM. I stayed away from RVM for sometime, only because I thought working with the systems version of Ruby was enough for me. As I got more involved with Ruby scripting and programming, I found myself needing a more robust installation that did not conflict with the systems version.
These steps are taken from RVM website.
They setup a nice script that you can get directly from GitHub. Run the following from your shell prompt.
Setup Your Shell
That is about it.