Main Toolbar > Select And Manipulate button
The Select And Manipulate command lets you edit the parameters of certain objects, modifiers, and controllers by dragging "manipulators" in viewports.
Note: Unlike Select And Move and the other transforms, this button's state is non-exclusive. As long as Select mode or one of the transform modes is active, and Select And Manipulate is turned on, you can manipulate objects. However, you must turn off Select And Manipulate before you can select a manipulator helper.
You can add these custom manipulators to your scene:
These features have manipulators built in, which you can use to change parameters on the objects:
IK Solver Properties Rollout (HI Solver)
Primitives with a Radius parameter have a built-in manipulator for the radius.