My favorite underappreciated XML language XUL (XML User Interface Language) could become more than a Mozilla utility with Prism. To quote the Prism site:
Prism is a simple XULRunner based browser that hosts web applications without the normal web browser user interface. Prism is based on a concept called Site Specific Browsers (SSB). An SSB is an application with an embedded browser designed to work exclusively with a single web application. It doesn’t have the menus, toolbars and accoutrements of a normal web browser. Some people have called it a “distraction free browser” because none of the typical browser chrome is used. An SSB also has a tighter integration with the OS and desktop than a typical web application running through a web browser.
In other words, with Prism you can write your own interface in XUL that shows and hides what you want. You can then use it, in theory, to create network applications without all the interface overhead of a browser. How far are we from the browser as OS?
Thanks to Peter for this.