Secure your Cloud files automatically before upload, with Cryptomator
Cryptomator is a free (for personal use) program that uses AES encryption to secure your files locally before they are uploaded to the Cloud.
You can use Cryptomator with OneDrive, Dropbox, Google Drive or any other Cloud storage provider. The application is not dependent to particular Clouds since it only encrypts files stored locally in folders that are synced with the Cloud.
A nice feature of Cryptomator is that it encrypts files individually, so that each time you make a change there is no need to sync all your files with the Cloud but only those modified.
Of course you don’t need to use the Cloud to protect your files, if you only like to protect some local folders.