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.
RubyMine 5.0.2 is available (released February 6, 2013, updated March 4, 2013)
Read what's new in RubyMine 5.0, download and try it. RubyMine 5.4 EAP is available (updated April 4, 2013)
Visit RubyMine 5.4 EAP page to download and try it.