When I started learning code and to build websites, I felt it very cumbersome to login into cpanel and upload PHP files. Hence I built my own file manager called HostBrowser[1]. It was a single PHP script. It had a lot of functionality that a lot of advanced file mangers have, like copy paste, compress files to Zip, extract Zip, copy-paste, directly download file from remote server, a code editor. The UI was inspired by that of phpLiteAdmin[2].
[1] https://github.com/anupamsaikia/HostBrowser
[2] https://en.wikipedia.org/wiki/File:PhpLiteAdmin_Main_Screen....
