Pure-FTPd is a free (BSD), secure, production-quality and standard-conformant FTP server. It doesn't provide useless bells and whistles, but focuses on efficiency and ease of use. It provides simple answers to common needs, plus unique useful features for personal users as well as hosting providers.
Pure-FTPd provides MySql, PostgreSQL, LDAP, and custom authentication. It can also run a script after an upload completes.
Pure-FTPd will compile and run on Linux, OpenBSD, NetBSD, DragonflyBSD FreeBSD, Solaris, Tru64, Darwin, Irix, HPUX, AIX and iPhone.
More information about Pure-FTPd can be found here http://www.pureftpd.org/