Demos are are written to show REBOL off in some way. Yes, you may learn something from their code, but their goal is to just look cool and show off. All demos will have a display of some kind, even if it's just a console.
Games are games. If you can play it, it's a game.
Tools provide some kind of useful functionality.
Idioms are are the little nuggets that show you the inner zen of REBOL.
Plugin scripts can run in a browser, provided it has scripting enabled. Right now, REBOL.org has not enabled any scripts to run as plugins. For more information on the REBOL browser plug-in, please visit the Plugin guide for developers
It's a one-liner if it fits on one line, it qualifies. You'd be surpised how much some of them do.
A function or a set of functions that can be called or included in other scripts.
A module is set of related functions, and perhaps data, that generally would define a context/namespace to avoid collisions.
REBOL protocols not network protocols
Dialects a.k.a. Domain Specific Languages; where REBOL really shines.
UI / GUI
GUIs (Graphical) User Interfaces
Internet Web stuff, HTTP, CGI, TCP/IP, email, etc.
Text processing Includes markup (e.g. HTML, XML) related processing.
Packages -- Multi-file scripts that may need installing.
Patches -- updated versions of mezzanines that ships with a standard REBOL distribution. Some of them will come from RT and others will come from users.
Broken -- Items listed here are known to have issues under one or more REBOL releases. They are included here so that people can fix them if they feel so inclined, and they may still have something to offer in any case.