NOTE: THIS IS OFFICIALLY INTEGRATED INTO DUPLICITY. PLEASE REPORT BUGS THERE ON THEIR LAUNCHPAD, THEY'RE GREAT PEOPLE
(see how I fit all three uses of there their they're in one sentence?)

https://bugs.launchpad.net/duplicity/+bugs

A duplicity backend for BackBlaze’s B2 storage service.

To install, copy to /usr/lib/python2.7/site-packages/duplicity/backends

Run with duplicity /local/folder/ b2://account_id@bucket_name/

When it asks for you password, enter your application key

If you don’t want it to prompt you for the key, run with FTP_PASSWORD=application_key duplicity /local/folder b2://account_id@bucket_name/

Note: requires duplicity 0.7+ and python 2.7. Older versions of Ubuntu and Homebrew have older, incompatible versions of duplicity and possibly python.