I’ve recently started to use blender’s texture paint system. It is responsive and , but the fact it only allows you to manage a single texture and not layers as, for example, Mudbox or “The Beast” Mari gets quite in my way 
If there’s any addon or project going on or already out there I’ll thank you guys a lot if you can tell me about it.
Thank you all!
Are you talking about painting in the 3d view? This is possible through individual material texture layers in Blender Internal material, each layer is an image mapped to UV. You can use GLSL to preview and interact in real time, and if you enable the Texture Paint Layer Manager in the User Prefs Addon panel, then you can make quick work of it in the 3d view. Quick tip though is that you need to set each image under the UV’s in the UV Image Editor before the painting will actually work.
and obviously you can save the painted image layers and use them in cycles.
it would be nice to have
http://wiki.blender.org/index.php/Dev:Ref/Proposals/UI/Mode_sensitive_outliner
Here ya go: http://ruesp83.com/image-layer/roadmap/
…unfortunately, progress is very slow. Lack of funding.
I’ll wait for Substance Painter, I guess. 
As noted above Fabio Russo is working on them and I am also interested on helping with migration (I have been in contact with him already). No promises on the time frame though, unless there’s a change of priorities it will possibly be after GSOC migration and pie menus, if nothing else comes up.
Psy-Fi, do you know if the current work Fabio has is 2d editor only or if it works with the 3d view as well?
It’s 2d only. I still haven’t checked it out entirely though. Code comments are also in Italian which will make this harder XD
That would amazingly smart if ever implemented.