To complement the web based FTP client (Net2FTP) mentioned here how about a PHP and Javascript based file manager to go with that. The file manager is called extplorer and is found here. This could be used in your app or portal to extend functionality.
The developer says you can use it to
- browse directories & files on the server and
- edit, copy, move, delete files,
- search, upload and download files,
- create and extract archives,
- create new files and directories,
- change file permissions (chmod) and much more…
You can even use eXtplorer to login to the FTP server (like net2ftp) and work as if you were using an FTP client. Access via WebDAV is also possible (requires some extra work and a database!).
Note you need a recent (> 4.3) PHP install and a recent javascript enabled browser