1. RubyMine

RubyMine is a commercial IDE for Ruby built on JetBrains' IntelliJ IDEA platform.

It is at the time of this writing the best environment to work with RubyMotion. RubyMine features context-based auto-completion, point-and-click debugging (on both the simulator and the device), inline documentation, and so on.

Please refer to the Getting Started with RubyMotion guide on JetBrains' developer website for more information.

2. TextMate

TextMate is a popular editor on OS X.

A RubyMotion.tmbundle plugin is available. It provides code completion and an integration with the build system. It is developed by Libin Pan and Berklee.

3. Sublime Text

Sublime Text is a relatively new editor for OS X, Windows and Linux that is gaining a lot of interest.

SublimeRubyMotionBuilder is a plugin that provides code completion and an integration with the build system. It is developed by Kentaro Hara.

4. Redcar

Redcar is an Open Source editor written in Ruby.

redcar-rubymotion is a plugin that integrates the RubyMotion workflow in Redcar. All features of RubyMotion are integrated. It is developed by Delisa Mason.

5. Vim

Vim is the most popular clone of vi. Vim ships in OS X. MacVim is a flavor of Vim for OS X that runs outside the terminal.

The builtin rake ctags task can be used to generate a tags file containing all the APIs the project can call into. This file can then be used to automatically complete API calls in the editor. RubyMotion uses Exuberant Ctags. Ctags is a format understood by a variety of text editors, Vim included.

Better auto-completion can be provided by using the snipmate-snippets-rubymotion plugin, courtesy of Rajeev Cyrus.

6. Emacs

Emacs is a popular text editor. Emacs ships in OS X.

motion-mode is a plugin that provides code completion and an integration with the build system. It is developed by Satoshi Namai.