Apps similar to MediaKnight include WP Download Manager, which is free. Other options are Trilobita DocVault. Between them they cover the web and self-hosting.
WordPress Download Manager is a Files / Documents Management Plugin to manage, track and control file downloads from your WordPress Site. Use Passwords, User Roles to control access to your files, control downloads by speed or by putting a limit on download count per user, block...
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DocVault turns WordPress into a document library. Upload a file once and its download link never changes: when you upload a new version, every link on your pages, menus and emails serves the new file automatically, and the previous versions are kept so you can restore them.
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