Lily Gizmos is a Blender add-on that allows you to easily create custom gizmos, i.e. viewport interactors/handles. This powerful tool lets users interact with parametric shapes or rigs in a very smooth way.
No coding is needed, whereas vanilla Blender requires python scripting to create custom handles. Just create an empty and turn on its Lily Gizmo in the Empty properties panel.
Gizmos can be customized – from their color to their entire shape, which can be imported from any mesh.
They can drive any property of an object or bone, including location, rotation, scale, etc.
If you are a developer yourself, you can add your own widget by just creating a new file in the Gizmos directory.