Arq

It's almost common knowledge that having your data backed-up is almost always a good idea.
As we are sure you already know, the vast majority of cloud-based backup and storage providers out there offer some sort of security features designed to keep your data out of harm's way.
This said, if you want to add an extra layer of protection to your cloud backups, then Arq is definitely one solution that should be in your top pickings.

One of the best applications of this sort

Already a popular app for the Mac for quite a while now, Arq is an efficient cross-platform application that also works on Windows and makes it possible for you to encrypt everything you backup on all major cloud storage providers with your very own user-defined key.
This said, the utility comes with full support for Amazon Cloud Drive, Dropbox, Google Drive, Microsoft OneDrive, AWS S3 and Glacier, Google Cloud Storage, SFTP and other S3-based services.
Quite interestingly, the app can backup any file of any size and can also backup all your external and network drives, if need be. Probably the most interesting fact about this useful tool is that it does not delete any old backups.

Novice-accessible and non-intimidating encryption tool for cloud backups

Subsequent to a swift and surprise-free installation process and upon launching the application, you are met by a simplistic and functional user interface.
As you can imagine, before you can use it to its full potential, you are required to create a connection with your preferred storage service which means having to enter the official credentials.
Worth mentioning is the application's de-duplication feature that, as its name suggests, makes sure that the same data is only uploaded once, thus minimizing the network traffic. In addition, you can also exclude files by specifying their name or exact path, set maximum storage budget, and limit the transfer rate speeds.

Offers an impressive level of 'freedom' and adds an extra layer of protection to your cloud backups

To conclude, Arq is an interesting and useful security tool that helps you effortlessly add a layer of protection for your cloud-stored data.
The app has a lot going for it as it works with a wide array of cloud storage providers and it is very novice-accessible thanks to its simple interface.
Even more so, it comes with a set of features like deduplication, support for encryption regardless of the file size and no time-limit to delete old backup records and that clearly make it stand out from other utilities of this sort.