This page describes getting your local environment ready for Ruby on Rails development.
For Windows users, check out Rails Windows Installer. This one-click installer will provide an environment with Ruby, Rails, Git, Sqlite, the DevKit, and SQLServer support. After the download is complete, you are ready to start writing and running Rails code. Check out their video for more details on the installation process.
The easiest and simple way of getting a Mac ready for development is by using the open source tool cinderella. Before you install it you will need to download Xcode first. Login with your Apple ID and then download the latest version of Xcode.
To start the process immediately run the below command after you get Xcode installed.
curl http://github.com/atmos/cinderella/raw/master/bootstrap.sh -o - | sh
The build will take about 45 minutes so go make yourself some coffee or tea while you are waiting.
Cinderella is a fully managed development environment for open source hacking on Mac OSX. It provides you with Ruby (1.8.7), Rails, Git, MySQL and a lot of other essential tools to be able to develop on your Mac. Go read up on the tools that it installs by clicking on the cinderella link.
Now that will get your environment setup, your next step is picking an editor that you are comfortable with. Some people prefer using an IDE and a good one for RoR development is Netbeans. You can download the IDE with just the barebones for Ruby development or you can get it with everything setup for Ruby, PHP, C++ and Java. Other people prefer to just use a text editor. Text editors alone have caused many debates between programmers. The three big ones are Textmate, VIM and Emacs. Textmate is the editor of choice for most RoR developers, but there are still plenty that stick with VIM or Emacs.