wzdftpd is an FTP server designed to be modular and entirely configurable
online using SITE commands.

wzdftpd offers the following features:
- Simple configuration file, supporting inclusions
- Online administration, using SITE commands
- Backends to store users/groups in different structures
- Modules: internal, using shared libraries, or external
  (scripts/applications)
- Users are virtual: you do not need to create users in system
- SSL/TLS support
- Server is designed to run as a non-privileged user to enforce security
- Server can detect ip changes (dynamic ips) and set ip and passive ip
  accordingly
- Cross devices operations (copy/move) (though can be slow)
- Logging support (compatible with the wu-ftpd standard)
- Designed for high performances: coded with C, multithreaded

WWW: https://sourceforge.net/projects/wzdftpd/