Redcar-debug is a project mainly written in RUBY and JAVASCRIPT, it's free.
The Redcar GDI is meant as a general debugger interface to allow integration of remotely attaching commandline-driven debuggers into the Redcar editor by Dan Lucraft™
It uses a variation on the builder pattern to create natively-ish looking frontends using Haml partials and the Redcar observer mixin to communicate between process, frontend and debugger model. Currently available models are for GDB and JDB, more will follow.