Select Hierarchy

shortcut Down in object mode" shortcut SHIFT + Down in object mode" to include the parents in the selection

Select Hierarchy is used to quickly select all children or parents of the selected object(s).
It aims to fully replace Blender's native Select Parent/Child tools, and comes with additional features, such as the ability to unhide and reveal children and parents, including recursively, and optionally including mod objects (that aren't parented), when selecting down.

Note

What makes this different from Blender's native Select More/Less, is that it works on the entire object selection, not just the active object, and that it supports optionally un-hiding hidden children or parents objects.

There's also a fading HUD, used to indicate if the top or bottom of a hierarchy is reached, and optionally if there are hidden parents or children left, that can be revealed and selected.

SelectHierarchy1 Selecting up and down the hierarchy until the top and bottom of the hierarchy is reached

SelectHierarchy1 Seleciing down, then up, then reaching top with hidden parent, selecting further up with unhide feature, and finally recursively selecting down and unhiding

Object Context Menu

Modes

SHIFT include parents as well

Using Select Hierarchy

Select Center Objects

Select Center Objects is used to quickly select all objects with geometry on the positive and negative sides or a chosen axis.

For instance, if you have a design in your scene, that consists of multiple objects, where some are at the center, perhaps positions along the Y or Z axis.
Other objects are then mirrors across the world X axis.
In such a case you can use the tool to very quickly only select the center objects - the ones that aren't mirrored across X.

Object Context Menu

Select Wire Objects

Select Wire Objects is used to quickly select all visible objets with a display_type set to WIRE.
Addons like Hardops or MESHmachine use wire objects to distinguish boolean operants from other objects.

Object Context Menu

Modes

ALT hide wire objects instead of selecting them
CTRL include empties as well