Duplicati is an open source « backup to cloud » software, which allows to backup your data to various cloud platforms, or simply through ftp or ssh.
I packaged the latest version for my Asustor 3102T NAS,
and submitted it for publishing through App Central. Meanwhile, you can download it from here : duplicati_1-1-1_any.apk
Update 14/11/2016: Now available in App Central, in the Beta section.
Have fun !