AppLock is a lightweight Android app that enables users to apply a lock on almost any type of file or app on their devices, preventing access to your locked apps and private data without a password. The most basic functionality of the security feature is to lock your Android apps so that nobody can access or uninstall them, but applock can hide pictures and videos, and even contacts and individual messages. With, you can create a specific PIN (or an app-specific PIN) that can then be used to lock down whatever applications you wish to secure.
Source: https://thehackernews.com/2015/09/android-applock.html