Speedbar is an emacs lisp program which allows you to create a special skinny frame with a specialized directory listing in it. this listing will have both directories and filtered files in it. you can then load files into your emacs frame, or expand the files to display all the tags that are in them and jump to those tags. you can also expand multiple directories into your speedbar frame. it supports file/directory trees, info manuals, eieio class browsing, project browsing, context analysis/autocomplete, eirc groups, xshtml, and vhdl. it can be rigged to display just about anything.

speedbar is now a part of cedet (collection of emacs development environment tools).