"It's a debugger for web pages, like FireBug (for FireFox) and Web Inspector (for WebKit-based browsers), except it's designed to work remotely, and in particular, to allow you debug web pages on a mobile device such as a phone."

vim plugin for ruby-debug integration

a helpful intro to ruby-debug and rails

"It’s a small tool (think Firebug for PHP) to provide profiling and debugging related information to developers without needing them to add a lot of programmatic overhead to their code."

helpful

helpful today at work

web-based debugging environment for rails apps - this could be promising