Closed-Source XUL Motors

xWidglets
http://xwidglets.secretgate.com
XUL motor in Java; includes UI designer; headed by Pierre Dezon

Ultrid
http://www.ultrid.com
XUL motor in Java; supports ten scripting languages; calls its XUL dialect XPML (eXtensible Programming Markup Language); headed by Andre and Pierre Morel

XMLFace
http://www.xesoft.com/products/xmlface
XUL motor in Java that lets you build Swing or SWT UIs; headed by Jon Lipsky

Xamlon
http://www.xamlon.com
XUL motor for Windows.Net; tries to support Microsoft's upcoming XUL-dialect called XAML (eXtensible Avalon/Application Markup Language); headed by Paul Colton

Mobiform XAML Browser
http://www.mobiform.com/xamlproducts.aspx
Vancouver startup; XUL motor for Windows.Net; tries to support Microsoft's upcoming XUL-dialect called XAML (eXtensible Avalon/Application Markup Language);headed by Ron DeSerranno

Zulu
http://zulu.netspedition.com
Toronto startup; XUL Motor in 100% Actionscript using Macromedia Flash MX; Headed By Ovi Comes

Bambookit
http://www.bambookit.com
Montreal startup; tiny Java XUL toolkit (less than a 100k) designed for applets or mobile devices runs on Java 1.1 and up; Headed By Louai Munajim; starts at US $699 for 1 dev license/1 website license and goes up to US $3,499 for 8 dev licenses/unlimited website licenses

eNode
http://www.enode.com
San Jose startup; Java XUL Toolkit for building Swing UIs; includes Web Services support and a XUL browser/sandbox