What are some alternatives?
When comparing FileZilla Server and Cyberduck, you can also consider the following products
vsftpd - Very secure FTP Daemon, a secure, fast FTP server for UNIX systems, including Linux.
FileZilla - FileZilla is an FTP, or file transfer protocol, client. It lets individuals transfer single files or batches to a web server. For many years, FTP was the standard for website design. Read more about FileZilla.
ProFTPD - The Official ProFTPD web site. ProFTPD is a high-performance, extremely configurable, and most of all a secure FTP server, featuring Apache-like configuration and blazing performance.
WinSCP - WinSCP is an open source free SFTP client and FTP client for Windows.
Serv-U FTP Server - FTP server software
Forklift - The most advanced dual pane file manager and file transfer client for macOS.