Smart Object Select is a blender addon, which is used to make smart selections of mesh objects.

It is possible to select by:

Name (Ctrl + F +S )
Select one object and set the split parameter and all object with the same name (all that match in the name before the split parameter) will be selected.

Volume 
Select one object and choose:
More (Ctrl + F +O) - The object and all objects that have the same volume and greater volume then this object will be selected

Less (Ctrl + F +V) - The object and all objects that have the same volume and less then this volume will be selected

Equal (Ctrl + F +E)- The object and all objects that have the same volume will be selected

Volume Match in % - Value to set how good match in volume it should be, 100% = perfect match and 0% no match at all (all will be selected).
Use fast volume calculations - With this option it will calculate the volume using each object's bounding box instead of the correct volume. Faster, but not as accurate.

Faces
Select one object and choose:
More (Ctrl + F +M) -The object selected and all objects that have got the same numbers of faces or more faces will be selected

Less (Ctrl + F +F)- The object selected and all objects that have got the same numbers of faces or less faces will be selected

Equal (Ctrl + F +N) - The object selected and all objects that have the same number of faces will be selected

With Ctrl + F you get up this menu

Smart Select (Ctrl + F +R) 
All objects that are most likely the same will be selected
Smart Match in % - Value to set how good match it should be, 100% = perfect match and 0% no match at all (all will be selected).

Remove Objects no faces
All objects that have zero faces will be deleted.

AutoRename Objects (Ctrl + F +A) 

All objects that are likely to be the same will be renamed with the same name.Starting at Part1000_PRT, Part1001_PRT and so on. 
Perfect for getting an order in an imported assemblies where each object has its own unique name instead of the same name on similar objects.

In Edit mode
Select by Congruent

Select one face in edit mode and by pressing "Select by Congruent", all faces that match the congruent criteria wil be selected. It is possible to change the tolerance for this selection, with the value below.

Good to know

Because some features require a lot of processing power, it can take a very long time for the addon to use the features. For example, select by volume.

It is strongly dependent on the object's mesh. More mesh information more time consuming.

Update 2024-09-11:
Version 2.4 A new function in edit mode where it is possible to select all Congruent faces that match selected face.

Update 2023-05-28:
Version 2.2 Some new functions and faster addon when using "Fast volume calculations"
Also shortcut is available by using Ctrl + F

Update 2021-09-19:
Version 1.9 two new functions "Remove Objects no faces" and "Autorename Objects"

Update 2021-06-15:
Version 1.8 works with Blender 2.93

Update 2021-03-28:
Now the Addon also work with objects that are instances of each other. Download new version 1.7.00.