For using Dropbox as a special remote, there are currently two choices:

* rclone supports the Dropbox API,
  so the [[rclone_special_remote|special_remotes/rclone]] can be used.  
  (Actively maintained)
* Alternatively, there is a dedicated special remote,
  <https://github.com/TobiasTheViking/dropboxannex>  
  (Last updated 2014)

At this time it's not clear which is better, so if you find one works
best, please comment below.