KeepSafe - Keep your entire photo library safely stored in an encrypted private cloud.
VeraCrypt - VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux.
AppLock (FOSS) - A privacy App lock FOSS application.
Easy Vault - Easy Vault: Hide Pictures, Videos, Gallery, Files is an all-in-one privacy protection application designed for those who want to lock and hide their private files.
Hexlock - Security app locker keeps apps private with smart profiles for any situation
Windows BitLocker - This topic provides a high-level overview of BitLocker, including a list of system requirements, practical applications, and deprecated features.