The influences can be viewed for each vertex, and can be changed either singly or set the whole selection to the same (six entries are all that is supported). I use this because it suits my work methods... I like to set assignments to each row of vertices along a joint chain, and tweak individual vertices after I start my test animations.
The tool is just for tweaking weights, like using the component editor, only more visual and with lots of menu shortcuts. You first need to use the smooth skinning tools to create a skinCluster before it will be of any use. Then you can select some vertices and run the tool, or run the tool and then select some vertices. There are two buttons, plus and minus, that enable you to walk through your selection viewing the current influences (joints) and their weightings for each vertex (only six boxes are provided). Changing the selection will reset to the first of a new selection list.
The weightings for the vertex can be adjusted by typing in a new value, or right-clicking on the box and picking one of the presets (0.0 to 1.0 in increments of 0.05). The influences can be changed by right-clicking on the current influence displayed and selecting a different name from the popup menu. The name "empty" is reserved for unused slots. The current active count and weighting total (excluding all "empty" slots) is displayed, as well as color highlighting when the total is not 1.0.
To send your changed values back to Maya, you click on either the "Update One" or "Set to All" buttons. Update One writes only to the currently selected vertex (from the selection set), while Set to All will write the values to all of the selected vertices. The utility of Set to All for me is that I like to select a ring of vertices along a joint chain and set the weighting the same, and this does that with a minimum of effort. No changes will be made to your mesh unless one of these buttons is clicked on.
And that's all it does. I have deliberately left out extraneous functionality because it would merely duplicate functionality already available in tools like the Comet Plugins https://www.comet-cartoons.com/ or the Component Editor built into Maya.
I have only tested the script on Maya 2011 (x64) and Maya 2009 (x64) using Windows 7. It may well work on other versions and platforms. I know it does not work on Maya 7.0 because some of the MEL commands changed after that edition. Like all tools, use it carefully, with plenty of backups, until you are satisfied with the functionality. While I use it here myself, I cannot guarantee it is useful or safe anywhere else, use your own judgement.
I have tested it with the recent release of Maya 2012, and it works fine, unless the uberverse melts away after all. I have uploaded the most recent version with this post. The permanent home for this is at https://www.weshowe.com/dlds/boneTool.html, you can check for updates there.