Arq is actually a standalone (incremental encrypted) backup tool, though they are now also offering their own storage. Arq can be used with Amazon S3, Dropbox, OneDrive, sftp, Google Cloud Storage, etc.
E.g. I use Arq with my Office 365 subscription that costs me Euro 1.38 per month (four year academic discount) for 1TB.
Arq only runs on Windows and OS X though. I would prefer to use something open-source, that runs on Linux. I won't be renewing my Crashplan subscription when it expires.
E.g. I use Arq with my Office 365 subscription that costs me Euro 1.38 per month (four year academic discount) for 1TB.