Twoftpd is an FTP server that strives to be secure, simple, and efficient.
None of the commands can cause execution of other programs, and the normal
model of execution does a chroot to the logged in user's directory
immediately after authentication. The name "twoftpd" comes from
the fact that there are two parts to the server: an authenticating front
end, which contains no file or data transfer code, and one of two back ends,
which contain all the data transfer code.

WWW: http://untroubled.org/twoftpd/