Dead/Neglected Open-Source XUL Motors

Perl XUL Project
http://perlxul.sourceforge.net/wiki
Perl XUL project shows how to use Perl and Tk in combination with XUL; GNU General Public License (GPL); headed by Matt Diephouse and Brett Estrade

Beryl
http://xmlgui.tigris.org
XUL motor in Java for building Swing UIs; includes UI designer; GNU Lesser General Public License (LGPL); headed by Jakob Wenzel

Xulux
http://www.xulux.org
XML Forms Engine using Swing; Apache License; Headed By Martin van den Bemt

SwingML
http://swingml.sourceforge.net
XUL motor in Java for building Swing UIs; GNU Lesser Public License (LGPL); Headed By Ezequiel Cuellar

KaXul, Uxul
http://webcvs.kde.org/cgi-bin/cvsweb.cgi/kdenonbeta/kaxul
XUL motor in C/C++ for KDE/Qt; GNU Lesser General Public License; headed by George Staikos

Purnama XUI
http://geekkit.bcit.ca/xui/web
XUL motor in Java for building Swing UIs; headed by Arron Ferguson

GUI Builder
http://www.guibuilder.de
XUL motor in Java building Swing UIs using XUL dialect dubbed "GUI Design Language" (GDL); includes scripting in Pnuts; Headed by Peter Koeker; includes a JavaDoc-like tool dubbed GuiDoc that automatically creates HTML documentation from Xul files; GNU Lesser Public License; (Note: German site ahead)

Ibex (formerly XWT - XML Windowing Toolkit)
http://www.xwt.org
Xul "Lite"; available as self-installing ActiveX browser plug-in; developed in Java; GNU General Public License (GPL); Headed By Adam Megacz

Java GUI Builder (JGB)
http://jgb.sourceforge.net
XUL motor in Java for building Swing UIs, GNU General Public License (GPL); Founded By Francois Beausoleil

Zaphod
http://zaphod.sourceforge.net
XUL motor in Java for building Swing UIs; BSD-Style License; headed by David M. Carr

KoalaGML
http://koalagml.sourceforge.net
XUL motor in Java for building Swing UIs; includes Pnats scripting engine; GNU Lesser General Public License (LGPL); Founded by Fabian Pena and Ricardo Zuasti

jXUL
http://jxul.sourceforge.net
Code Drop from the book "Essential XUL Programming"; GNU General Public License (GPL); Founded By Vaughn Bullard, Kevin T. Smith, Michael C. Daconta; Dead Since October 2001

Axualize
http://axualize.sourceforge.net
XUL motor in Java for building Swing UIs using Sun's long-term bean persistence XML format (Java Spec #57); also includes an XML scripting engine; GNU Lesser General Public License; Founded by Russell White

Xybrix
http://www.jbrix.org/kits/xybrix/overview.html | http://sourceforge.net/projects/xybrix
Java Xul motor for building Swing UIs dressed up in Kunststoff L&F; includes XForms support; MIT License; Founded by Jim Wissner; Frozen since October 2001 at version 0.1

Proto
http://www.pierlou.com/prototype/
Xul forerunner, builds Swing UIs from XML descriptions and supports scripting in Javascript or Tcl; Founded By Pierre Morel; Frozen since 1999

MotLib.Net
http://www.dilascia.com/motlib
Tiny XUL Engine in C# for .Nyet using Windows Forms; First Published in MSDN Magazine (November 2002); Founded By Paul DiLascia; Frozen since 2002

XUL2GTK
http://www.phppatterns.com/index.php/article/articleview/48/1/2/
XUL Motor Prototype in PHP for GTK; GNU Library General Public License (LGPL); Started By Harry Fuecks