Since January 2011, NFTP has been also released as open source software. If you don't want to compile NFTP, see below for the link to precompiled releases.
Precompiled NFTP releases can be downloaded from its main site: http://http.ayukov.com/ftp/nftp. This directory also contains beta (preliminary) releases, marked by .b2, .b4 etc. Version 1.72 and below require registration: after 60 days of use they display 10 sec registration reminder when you login to site. You can get registration code for free to get rid of this reminder. You can no longer buy NFTP license.
Older versions are also available if you really want them (they are not supported though).