Inheritance selfmade or reinventing wheel
From some staring at your code:


Do not declare var in an if block, it gives the wrong impression. I would just declare it on top, something like this:

//Define namespace
var SimpleJSLib;
SimpleJSLib = SimpleJSLib || {}; 


As far as naming, since SimpleJSLib is not a constructor, it should not start with capital S. The name JSLib is not very informative beyond what language it is writen in..
I know that for some _ in _protected means "private", but I agree with Crockford that this convention should be avoided
Now a big one: you broke support for instanceof operator, that's just wrong
Furthermore, you kind of broke support for prototype, you are also not using hasOwnProperty anywhere when you construct objects
And, JS has a perfectly valid constructor, but you decided to have your own construct
Finally, this will be messy once you want to start serializing with JSON


Honestly, read this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript and abandon your code. I would not want to maintain code that relies on this.