Dating back to the days of Windows 3.0, File Manager was an application using the multiple-document interface to display the contents of several folders within one window.
File Manager served as the precursor to the modern day Explorer interface that debuted with Windows 95. Now, Microsoft has made the source code of File Manager available for all to use under the MIT License, and it still can be run on all recent versions of Windows, including Windows 10.
Officially, File Manager was supported from 1990 to 1999. Even though Explorer was introduced to Windows 95, File Manager was still included by default and remained apart of Windows 98 as well as Windows ME.
The original version of File Manager was a 16-bit program that only supported DOS filename conventions. Long file names and names containing spaces were displayed using only the first six characters with a tilde appended to the end of the string along with numbers to differentiate between files with similar names. A 32-bit edition was released for Windows NT 3.1 that corrected many of the naming issues.
The replacement to MS-DOS brought many of the features that are now taken for granted. Creating, renaming, moving, copying, and deleting files from a graphical user interface were among the revolutionary features of the time. Instead of opening endless numbers of windows, File Manager allowed for navigation through directories and basic file management tasks in a clear cut and organized manner.
For those wishing to try out File Manager on Windows 10, there have been some slight changes made to take care of minor bugs. The most notable change being that there is support for 64-bit operating systems. Visit Microsoft's GitHub page to download the source code of File Manager. If you have trouble building from the source for your operating system, you can try this fork that is confirmed to run on Windows 10 without any anomalies.