"Simple and secure privacy protection
Cloudfogger encrypts your data on the local device before it gets uploaded to the cloud. That guarantees that Dropbox and others never get access to the content of your files."
"CloudMounter is a must-have tool for laptop users with low-capacity SSD-drives. You can easily mount most popular clouds as disks without having to download online files on the hard drive. As well as secure cloud files with data encryption. Choose one of your Dropbox, Google Drive and OneDrive accounts and manage them in Finder for free."
BoxCryptor is a cryptographic virtual harddisk that encrypts all data on-the-fly using the AES-256 standard. Encrypted data is stored in an arbitrary directory of your choice, e.g. one that is synced to the cloud like your Dropbox folder.
"They make it simple. We make it secure. Encrypt your files before they sync to Dropbox®, Box®, Google Drive™, OneDrive® or any other folder on your devices."
Tahoe-LAFS is a Free and Open cloud storage system. It distributes your data across multiple servers. Even if some of the servers fail or are taken over by an attacker, the entire filesystem continues to function correctly, preserving your privacy and security.