title: How can I install different versions of Rails and keep the existing ones?
body: <p>I had Rails 2.3.5 installed, and wanted to upgrade to 2.3.10 as a stepping stone to Rails 3. I thought running <code>gem install rails -v=2.3.10</code> would install 2.3.10 and keep 2.3.5 as well. But now when I do <code>rails -v</code>, it only lists Rails 2.3.10. How can I install different versions of Rails and keep the existing ones?</p>