From the RubyOnRails weblog:
RadRails is a project to build a cross-platform IDE for Ruby on Rails using the Eclipse platform. It’s still very early days, but they have an alpha out you can play with.
Hm. I for my part really enjoy not using the tools I used for Java development when doing Rails projects. Especially if it saves me some hundred MB of RAM ;-)
But - as long as it attracts more users to Ruby and Rails - fine with me :-)