This is simple cut of standart Paint Weights Tool Window, plus added some functions.
In my game-developing workflow it's very useful, and I guess that it can be useful not only in game developing and in all skining jobs.
Principles of use:
When you paint weights you often want that weights not run to some unknown joints. In my system I use virtual set of joints that you want to paint. To begin painting you must select one or more joints and run "paintWeights". Script find mesh that skinned by this joints, select it, activate Paint Weights Tool, and set painting to first selected joint. If you selected two or more joints, script set "hold" to other joints in this skin. If you want to unhold all joints of this skinCluster, press "unhold" button, if you want to hold back joints that are not in virtual list, press "hold". To paint the next joint in your virtual list, press "next joint".
Remember that you are always working with "virtual list" of joints that you set each time when you select joint(s) and run "paintWeights();". Buttons "next joint", "hold" and "unhold" work with this list. If you don't want to set this "virtual list" you can select mesh and run "paintWeights();".
Virtual list saves in global string variable, and if you set it once, you can clear it only if you restart maya. If you want to clear this list you can also select main of your skinned joints, go to Edit > Select Hierarchy and run paintWeights() again. Now all joints of skin added to virtual list of joints, this is the same if virtual list doesn't exists.
Little feature - after weighting you can choose Select Tool or any other, do what you want and then to paint same joints just move slider (or touch any other control) at small distance and weighting resume.
Use checkbox "0.1x" to scale range of slider from 0 - 1 to 0 - 0.1. Button "color" toggle color feedback.
Happy weighting! :)