AppLock (FOSS) - A privacy App lock FOSS application.
KeepSafe - Keep your entire photo library safely stored in an encrypted private cloud.
Hexlock - Security app locker keeps apps private with smart profiles for any situation
MaxLock - MaxLock is an applocker based on the Xposed Framework.
Hide Secrets - Hide Secrets is an app that allows hiding everything they deem confidential on their smartphone.
Viso - Beautiful minimal image viewer for MacOS