If you are planning to build a website that would primarily act as a download manager / file manager / file transfer management portal etc. Then the best combination you could choose is WordPress CMS to be clubbed with any of the available file manager plugins. WordPress CMS gives the solid framework to build your download manager website on and also manage the entire portal from the backend / admin panel.
Below are the selected best plugins that will help transform your normal wordpress blog into a complete file management system.
Let us know your thoughts on these plugins and also feel free to recommend if you have used any better plugins that could serve the purpose for building a download manager on WP.