TangentTool:

Change tangent type of animCurves. Kind like maya's tangent type button in GraphEditor.

The difference is that you can do this via timeslider. No need to open GraphEditor.

How to Use:

1.Open Keyframe tools, click on Tangent tool title if it's folded.

2.If you just want to correct overshoot, that is ,to auto-smooth selected animcurves, just press the "Correct Overshoot" button and done.

3.If you want to change key tangent types, preselect a tangent type in the second row.

4.Press any one button of the last two rows to actually change the tangent types.

Some UI elements:        

    Correct Overshoot Button: Auto smooth animcurves. Will set tangent type to flat if it is a peek value compare to prev & next keys, will make it smooth type and tweak the tangent angle if it is not a peek value.

    Tangent type buttons:Kind like the tangent type buttons of GraphEditor, but these button is just pre-selection, does not actually change the type. Use one of buttons below to actually do that:

         LEFT Button: Change the tangent type of the previous keyframe. Will change current key tangent type if there is a key at current frame.

         BOTH Button: Change the tangent type of both the previous & next keyframes.

         Right Button: Change the tangent type of the next keyframe.
         ALL Button: Change tangent type of all animation of current selected objects .
         Selected Range Button: Only change tangent type of the animation of current selected objects in the selected time range.