Here is a great solution for anyone who wants to encrypt their data before putting it onto the cloud.

It's an open-source encryption software for PC, MAC, Linux, Android, and iOS. So every common plattform is supported.
How is it encrypted?
In short:
You get a realtime de-/encrypted container.
the password: scrypt
the files: AES-GCM (256 Bit)
(the filenames are also encrypted beforehand)
See the full documentation on that here: https://docs.cryptomator.org/en/latest/security/architecture/

Note
There are multiple files generated. good for cloud sync.
The structure looks for similar to the files and folders created with ENC DataVault by ENC Security
You get a "light" Version (which enables AES 256 bit) of that software with buying a Sandisk Cruzer USB Stick. I've bought the pro version allowing multiple, military-grade AES 512 and also AES 1024 bit containers.
=> cryptomator has a better usability
Use cases
In my case, I use it to safely share and access data between my windows pc, linux (ubuntu) and android smartphone.
On mobile, you get the option to sync your taken pictures encrypted into one container. for convenience, there is the option of entering your credentials to encrypted containers via fingerprint.
It would be possible to share cloud storage with other family members and keep private data protected.
You could also just encrypt your files locally on an external disk.
About the company: Skymatic GmbH
It's born as a german startup with the idea: there are a few cloud encryption tools available... but no one has made their code open source to be transparent and also more secure.
They also provide company licenses for implementing their technology into your own software or you can get an enterprise solution for encrypted file storing and sharing: cryptomator server https://server.cryptomator.org/

Pricing
Nov 2019:
PC / Linux / Mac: Pay what you want

Android and iOS:


right now there is a discount for 5,99 EUR