What needs to be fixed with prototypical OO?

Writing code that utilizes that specific feature of JavaScript is cumbersome.

It's one of the reasons why Prototype.js was created, and one of the reasons that people use CoffeeScript, don't you think?

No. If anything you need to have a better understanding of JavaScript's prototyping behavior to write good CoffeeScript. It's only cumbersome if you're not familiar with it.

I'm not sure what you mean by "fixing" javascript's OO implementation, but I guess you could have a look at qxoo, qooxdoo's oo engine re-packaged as a standalone project.

https://github.com/fjakobs/qxoo/

Thanks! It looks like a full-featured solution, and it's even a commonJS module.

Thing is, that CoffeeScript solves the most common pain though (the *.prototype syntax), and the chasm between that and interfaces, singletons, private members, etc., might be too big for the standard use case.

As of ECMAScript 5 you can build inheritance chains without constructor functions and *.prototype objects. It is simple enough without any framworks (https://gist.github.com/1558929) and it is just a bit more verbose than CoffeeScript classes (https://gist.github.com/1671263)