RubyMine — is the dedicated Ruby and Rails IDE providing intelligent Ruby code editing assistance and tools for web applications development with Ruby on Rails. Find more at official web-site. IntelliJ IDEA is providing similar functionality with the Ruby Plugin installed.
Try RubyMine 4.0
RubyMine 4.0.3 is available (released Feb 15, 2012, updated Apr 18, 2012).
Read what's new in RubyMine 4.0, download and try it. RubyMine 4.5 Early Access Program is now open.
Visit the following pages to try early builds of next RubyMine release: