Extra controls
 

I'm building the options panel for my addon.
If I want add controls that are not available with xml as the trackbar (just like this) what can I do?
I know that must use an external library, but wich is it?

You mean the Slider widget? The Blizzard UI uses XML for all of their windows/options. I'm fairly positive you can do it. ;)

You don't need to use a library to make config windows. And you don't have to use XML (you could write it all in Lua).

That said, I create my larger, more extensive option windows use AceConfig. If the addon only has a few settings, though, I write it from scratch.