This is a Heroku buildpack for adding lftp to your application.
More likely, you'll want to use it as part of a larger project, which needs to use lftp. The easiest way to do this is with a multipack, where this is just one of the buildpacks you'll be working with.
$ cat .buildpacks
git://github.com/heroku/heroku-buildpack-ruby.git
git://github.com/niteoweb/heroku-buildpack-lftp.git
$ heroku config:add BUILDPACK_URL=git://github.com/ddollar/heroku-buildpack-multi.git
This will bundle lftp into your instance without impacting your existing system.
$ git clone http://github.com/niteoweb/heroku-buildpack-lftp.git
$ cd heroku-buildpack-lftp
$ heroku create -s cedar
...
$ heroku plugins:install https://github.com/heroku/heroku-repo.git
$ heroku plugins:install https://github.com/glenngillen/heroku-exit-status.git
$ heroku config:add BUILDPACK_URL=http://github.com/kr/heroku-buildpack-inline.git
...
$ git push heroku master
...
$ heroku run "lftp -v"
LFTP | Version 4.5.1 | Copyright (c) 1996-2014 Alexander V. Lukyanov
...