wzdftpd offers the following features (and the list is constantly changing):
Free - wzdftpd is distributed under the GPL
RFC compliant !
Server runs in user mode, thus does not need root privileges - on the other hand, it is not designed to use system users permissions, it uses its own user database and permissions.
Simple configuration file
Online administration, using SITE commands
Backends to store users/groups in different structures
Modules: internal, using shared librairies, or external (scripts/applications), and protocols
Powerfull event system
Job scheduler, also known as crontab
Users are virtual: you do not need to create users in system
Support for UTF-8: unicode filenames. wzdftpd is unicode compliant, on all supported platforms
Large files (> 2 GB) support, on all platforms
SSL/TLS support, using either GnuTLS or OpenSSL
IPv6 support (experimental)
win32: can auto-register as a service, unregister, start/stop
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