what’s a good FTP system to use for clients

WP: lastest version
URL: https://www.modinedrafting.biz

I wanted to have some type of an file transfer protocol set up within the site so clients could log-in, and FTP drawing files to me or I could FTP drawing files to them. I have set up a “Client Log-In” page and also have the plugin’s, Pages Link To and Peter’s Login redirect installed but not activated. I’m still trying to figure out the best way to do this FTP for the clients. If I set up pages for different clients, how do I integrate a FTP within the website for this file transfer. My mind is pretty boggled about this so any suggestions would be appreciated.

Thanks