Development Tools

REBOL mode for Emacs
Correct indentation and styling for REBOL coding in Emacs
http://www.rebol.com/tools/rebol.el

Rebol Unit
A unit testing framework for REBOL.
http://rebol-unit.sourceforge.net/

STEEL
An Integrated development environment for REBOL.
http://www.rebol.it/steel/

VIM Syntax Files
Syntax highlighting in the VIM editor for REBOL source.
http://www.eandem.co.uk/mrw/vim/syntax/