Sash and SashXB

Using XML, HTML and Javascript you can create appplications on Windows (Sash) or Linux (SashXB). The SashXB projects uses Mozilla and Gnome. The checkers demo application is even cross platform. While it's not a goal of Sash if you stick with HTML and other cross platform extensions (Jabber) you can achieve it.

Wired article:
http://www.wired.com/news/linux/0,1411,51476,00.html

Sash Web site:
http://sash.alphaworks.ibm.com/

SashXB Web site:
http://oss.software.ibm.com/developerworks/opensource/sashxb/