BoxCryptor - Boxcryptor encrypts your sensitive files before uploading them to cloud storage services like Dropbox, Google Drive, Microsoft OneDrive, Box, and many others.
Cryptomator - When it comes to saving your files on a cloud server, it is important to ensure the security of those files. Keeping your delicate files out of the wrong hands can save you a lot of time and hassle. Read more about Cryptomator.
Mega - Secure File Storage and collaboration
VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
Tresorit - Encrypted cloud storage for your confidential files. Using Tresorit, files are encrypted before being uploaded to the cloud. Start encrypting files for free.
Encrypto - Encrypto lets you encrypt files before sending them to friends or coworkers.