There's another project like ptl, called xulruner. It seems to have started with firefox 1.5, or about last Spring. It contains common controls like buttons, text boxes, and check boxes. It also looks to include file selection dialog boxes and maybe a spelling checker and corrector.
I think the major difference between ptl and xulrunner is that xulrunner has a special xml vocabulary called xul, which it uses to define the gui (graphical user interfaces) for the programs. Ptl just uses html, so the programs can interchangeably run offline, or over the web, just like any other web application. The other advantage of ptl just using html instead of xul, is that you don't have to learn a new language. And we don't have to support the overhead.