Cryptomator is a free, open source, client-side encryption for your cloud files.
Cryptomator lets you make encrypted versions of folders and files suitable for storage in the cloud, so that services such as Dropbox, Google Drive, Box.com, OneDrive and others are not able to read the contents of your uploaded files.
Rather than rely on cloud storage safeguards, Cryptomator encrypts your files before they even reach the cloud. Encrypting files locally means files with sensitive data stored in the cloud can’t be readily accessed, even if someone were to get to them.
Cryptomator can be installed on Linux, Mac OS X, Windows, Android, iPhone and iPad.
Proprietary applications it could replace: