Bone Widget is a blender add-on to assist with making custom bone shapes. It has an editable library of shapes that make it easy to apply to any rig.

It ships with many shapes pre-made but you can also add your own to the library to make rigging easier.

Installation:
Download the zipped code here from Github.

In Blender, open Preferences->Addons->Install. Navigate to where you saved the zip file and click install.

Enable the Addon with the checkbox.

The UI will appear in the properties panel (n panel) in the 3d viewport.

UI Panel
Shape:
This is the active shape from Bone Widget Library. Choose the shape you want to add from the list here.

BW Specials Menu:
drawing

Add to Widget library
To add a mesh object to the library, select a mesh object and click this button. Make sure you give that mesh object an appropriate name before adding.

Remove from Widget Library
This will remove the active shape from the library. Select the shape you want to remove from the list. And click this. Boom, it is gone (forever!).

Creating a Widget:
Create:
Select a bone (or bones), choose the shape from the drop down menu, then press create. This will create a widget object for each of the selected bones. The widget objects will be placed in the collection that is specified in the user preferences.

Redo panel
drawing

Scale to bone length:
When enabled the Global Size will be multiplied by the bone length. (ie – the widget will be relative size to the size of the bone) With this disabled, the Global Size will be in Blender units.

Slide:
This will slide the position of the widget along the Y axis (or length) of the bone. 0.0 is at the head of the bone and 1.0 is the tail. (negative values are possible too)

Rotation X/Y/Z
You can rotate the widget by these values at the time of creation. This can save you from having to jump into edit mode to rotate a widget to better align with your situation.