What are some alternatives?
When comparing FileZilla Server and Gene6 FTP Server, you can also consider the following products
vsftpd - Very secure FTP Daemon, a secure, fast FTP server for UNIX systems, including Linux.
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.
Serv-U FTP Server - FTP server software
Titan FTP Server - Windows FTP Server with SFTP and SSL. Includes events automation.
Baby FTP Server - The simplest FTP server to setup. No authentication required.
Microsoft IIS - Internet Information Services is a web server for Microsoft Windows