wzdftpd is a portable, modular, small and efficient ftp server.
It is designed to be run as root or non-root, It supports IPv6, SSL, and is multithreaded. Server is fully configurable online using SITE commands, and implements the latest RFC extensions to the FTP protocol.
Features are: flexible user management, ACLs, virtual users/groups, security, speed, bandwidth limitation, per command authorization, virtual directories, dynamic ip changes auto-detection, etc.
It includes several authentication backends, is easily scriptable and provides a powerful event-driven system to extend the server.