SafeMonk is described as 'Dropbox + Security Made Simple. SafeMonk is the only solution for Dropbox that is both tapproof and does not break the simplicity and functionality of Dropbox' and is an app in the Backup & Sync category. There are four alternatives to SafeMonk for a variety of platforms, including Windows, Mac, Android, Android Tablet and Chrome OS. The best alternative is Boxcryptor, which is free. Other great apps like SafeMonk are EDS (Encrypted Data Store) (Freemium, Open Source), SharedSafe (Free Personal) and Safebox (Paid).
Safebox encrypts and syncs files with your Cloud folder. Thanks to generated keys, no more remembering passwords and dealing with strength of passwords. Create separate keys for shared folders and start collaborating. Crypto code is opensourced.