In Ruby, a Gem is a way to package and distribute programs and libraries.
This appendix gives instructions for installing Ruby and the AppFog Gem on various common platforms. The Ruby packages described are those easily installed, except on Macintosh, where Ruby 1.8.7 is preinstalled. These versions of Ruby are not typically used for serious Ruby development, but are adequate for running the AppFog command line tool.
If you are interested in Ruby development, see the last section, The Ruby Version Manager. In addition to the AppFog Gem, you will also need the Sinatra Gem to use with the examples in this book. Sinatra is a free and simple web application framework built on top of Ruby. You can find out more information about Sinatra at http://www.sinatrarb.com.