6 steps to set up a rails development environment on OS X:

* install gcc pkg from https://github.com/kennethreitz/osx-gcc-installer
* install homebrew[1]:
  `/usr/bin/ruby -e "$(/usr/bin/curl -fksSL https://raw.github.com/mxcl/homebrew/master/Library/Contributions/install_homebrew.rb)"`
* install rvm:
  `bash -s stable < <(curl -s https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer)`
* install ruby
  `rvm install 1.9.3`
* install rails
  `gem i rails`
* start a project
  `rails new myproject`

[1] Use `brew` command to install whatever database engine you need, ie `brew install sqlite`