DirSplit

DirSplit is a tiny and portable application designed to automatically sort all files from specified directories into multiple subfolders by the number of items.
It doesn't include any configuration settings and can be used even by those with little or no experience in file management software.

Portability perks

The entire tool's packed in just one executable file that you can copy in any location on the disk or to a USB flash disk to carry it with you when you're on the move and directly run on any machine without previous setup.
Apart from the new subfolders, it doesn't create anything else on the computer. Plus, it doesn't modify Windows registry settings or need libraries or other components to work properly. If you want to uninstall it, it's only necessary to delete its .exe.

How it works

At startup, you're welcomed by a standard folder view that asks you to locate a directory whose containing files you want to sort. In the following step, you can indicate the number of preferred items to keep in each new subfolder. The task is immediately performed afterward.
The new subfolders are created within the specified directory and they are numerically incremented (1, 2, 3..). The containing files are now moved in the new subdirectories in sequential order and retain their original names.

Evaluation and conclusion

Unfortunately, the utility didn't perform as expected in our tests. We ran multiple scenarios with varying number of items for each subfolder. However, some files remained in the root directory on task completion and their position remained unfilled in the subdirectories.
We must also keep in mind that DirSplit hasn't been updated for a long time. Too bad that it doesn't make room for customization regarding the file and folder sorting method.