HandTool is a MotionBuilder Plugin for creating procedural animation for fingers and hands, created by neill3d, the plugin is available for download with some instructions on its use within MotionBuilder. More information and a download for HandTool Plugin for Procedural Finger Animation in MotionBuilder can be found here.
“The plugin works only with FK elements of Control Rig. A character must be chosen as a current one in CharacterControls window and have assigned control rig input Ctrl Rig In.”