rbenv is an alternative to rvm for managing your Rubies. You can find some articles comparing the two. In general, rbenv is more lightweight without overriding the cd and gem command which rvm does and their similarities outweigh their differences. Here is a great article written by Jonathan Jackson about the two solutions.
For Mac users, you could install rbenv using Homebrew. Otherwise, you need to checkout the repository on GitHub.
Eureka! 