Use the Secure File Transfer Protocol, originally a sub-protocol of the Secure Shell (SSH) protocol, as a standalone protocol that established directly on TCP instead of SSH.
This FTP server / client is really simple; it doesn't have any encryption and authentication stuff.
Based on the SFTP implementation in OpenSSH, specifically sftp(1) and sftp-server(8).
Server depends on xinetd(8) and sftp-server(8) (OpenSSH). Client depends on nc(1) and sftp(1) (OpenSSH).
Setup the server by deploy the provided xinetd configuration file, modify it to fit your needs, then restart xinetd. In the client, deploy file sftp-ssh-to-nc.sh to some where you could easily find or under the PATH; connect to server using sftp -S <path/to/sftp-ssh-to-nc.sh> [-P <port>] <server-address>.
Alternately, the sshfs(1) can also be used as client; mounting from the nsftp server is possible via sshfs <server-address>:<path> <mount-point> -o directport=<port>.