Most FTP clients work with FREEDOME VPN.
FTP clients and servers work in two different modes: active and passive. To be able to use an FTP client with FREEDOME VPN, you must configure the FTP client to work in passive mode. Nearly all FTP clients can be configured in this way, and, in fact, many of them have nowadays the passive mode set as the default value.
Note, however, that there is one common exception: the command-line FTP client included in Windows cannot be used even if it is set to passive mode as it will automatically switch back to automatic mode when a file transfer or directory listing is attempted.