Google Play Identical Files Finder Android application.
The main idea was to have a very small size application (apk size is ~1.5MB), to not waste to much space on disk.
Also the application can be moved to external SD card, to save space of internal phone/tablet storage.

It works for all Android v4.0+ phone and tablet devices .

Here is the detailed description about how to use the application.

Step 0

Only if you have Android v6.0+ .

First you have to allow access to READ/WRITE photo, media and files.
For older versions of Android it is done/asked when you install the applications.

Step 1

Here we select the folders we want to scan. We can select the entire internal and/or external storage, or can go one level below and select specific folders.
Also we can filter the files by size. If no minimum and maximum size are set, all the files will be search.

Step 2

Start to scan every selected disk and builds groups with files having the same size.

Step 3

No action is required for this steps. It just shows you the progress status.

Info about total number of groups having files of the same size, how many files we have in the current group, size of each file in the current group.

Step 4

Select files that we want to delete. For each group where we have selected at least one file, the color associated with the group will change.

We can sort the groups by files’ size  or by number of files in group ; both are in ascending order.

We can unselect or select all files.

When we decided what files we want to delete, just press DELETE button.

Step 5

Confirm that this is the list of files that we want to delete. Info related to the number of files and the total disk size that will be freed are provided.

Step 6 (Android v4.4)

Only for Android v4.4.* (KitKat)

On android version v4.4.* applications are not allowed to write/deleted in other folders except the folder associated with respective applications. So, we can not delete any file stored here. The list with such files are provided, and they have to be deleted connecting the phone as storage device to a PC.

Step 6 (Android v5.0+)

On some devices with Android v5.0+ the files from SD card can be added/deleted/modified only after extra permissions have been added. Such situations are detected by the application and will ask you to grant access to modify data on SD card. After providing the SD Card root the files will be deleted.