What? OSX has shipped with (some version of) Rails since Leopard. You don't need to install a compiler or compile anything to use Rails on a Mac. It comes with sqlite3, too.
$ /usr/bin/rails
Rails is not currently installed on this system. To get the latest version, simply type:
$ sudo gem install rails
You can then rerun your "rails" command.
> The basic database program that Rails uses is SQLLite3, and you will need to install this to work with it.
yet Tiger had sqlite3 already.
What's more, Ruby is installed already. One can 'gem install rails' and have the latest version landing in /Library/Ruby/Gems
While this is technically true, it's important to note that it's not usually desired.
You should be running a fairly recent version to keep up with patches or match your server, you should be running RVM so you can keep a gemset and use bundler, and you should use homebrew to make installing other packages easier.
Not that any of that is difficult, and you're right to a degree: you can get started learning using one command and go from there.
Added bonus: running sudo gem install rails spins for 20 minutes then dies with some cryptic error message.
At least that was what happened when I tried to install rails on my brand new macbook air.
To be fair though, open source software hates me. This has been pretty much the same experience I've had every single time I've tried to install anything with gem install, apt get or yum install. On every flavor of linux/unix on any box I've ever touched.
