My long-time favorite Java editor JetBrains/IntelliJ IDEA has added a Ruby plug-in that supports Rails. My initial reaction is that the vitally important quality of code completion is well below that of both Ruby In Steel and Komodo. Don't be too excited by the presence of the Analyze and Refactor menus either -- they're non-functional (or at least I couldn't get them to work).

The little "ruby" icon beside 'def HeloWorld' navigates to the view for the action -- that's pretty slick. You can generate Rails entities (controllers, etc.) via right-click context menus and you can Rake from within IDEA.

My quick feeling is that the plug-in, while welcome, seems to fall well short of the functionality in Komodo and Ruby In Steel much less the full array of functionality available in IDEA (or even ReSharper).

I wonder if anyone else is working on a Ruby IDE.