This if my first "true" Mac OS X development inroad (not counting Python and UNIX-like things I've done in the past). Following the success of the HP-12C emulator for Web, and having heard that it was relatively easy to convert a HTML page into a Dashboard widget, I decided to give it a try. Tou can download the widget here.As I have state several times in the past, desktop applications should be developed in interpreted languages these days, instead of using 90ish things like C++, Java or .NET. And the Mac OS X widgets were really architected in the right way. A widget "application" is nothing more than a HTML "page" that really governs applet's appearance. That page in turn refers to Javascript and/or CSS additional files.
Almost everything that Web developers are used to in Javascript, indeed works in the widget context, like keyboard and mouse events. Things that don't fit in the model like pop-ups, cookies etc. simply do nothing instead of raising errors, so in general the HTML widget remains testable inside a normal browser. And the most important, preexisting HTML and Javascript code is easily reausable in widget environment.
As anyone would expect, the Javascript code in the widget context has more privileges than in browser context. It can invoke system commands, and can call Cocoa (Objective C) methods.
Who knows, maybe I try now to convert this applet to iPhone...