Are there any good JavaScript frameworks out there which primary audience is not web programming? Especially frameworks/libraries which improves the object orientation? The framework should be usable within an desktop application embedding a JavaScript engine (such as Spidermonkey or JavaScriptCore), so no external dependency are allowed.
Objective-J(avascript) is one. Is that the kind of thing you are looking for?
The most widely known one is XULRunner from Mozilla. This is framework that FireFox and Thunderbird are built on.
https://developer.mozilla.org/en/XULRunner
Although not strictly javascript only, it incorporates a host of technologies closely tied to web for the purposes of building desktop applications.
Have you looked at Adobe Air? It allows you to use JavaScript/AJAX to write Desktop applications.
As far as "improving object orientation" goes, Javascript is already great. You just need to get used to thinking in prototypes instead of classes.
After reading Douglas Crawford's great page on prototypal inheritance I really started to enjoy working with javascript. (He also has a page on class inheritance if you must use classes.)
Edit: If by asking for a framework you also mean, helpful libraries that don't use the DOM, you might be interested in Functional Javascript.