BackupSheep plugin integrates with existing backup plugins such as UpdraftPlus(free/paid) and automates files and database backups using smart scheduling and the ability to push your backups to remote storage accounts.
This is a very simple plugin. You select folders and then upload documents (even via FTP) and your visitors can download them. You can shortcode the folders selected for download.
FileOrganizer is a plugin that helps you to manage all files in your WordPress Site. FileOrganizer provides you the ability to edit, delete, upload, download, copy and paste files and folders.