There are many custom libraries used in Android Development. These libraries are used to reduce the redundant code and save the time of a programmer. Below are the most used libraries in Android development. ButterKnife library is used to inject views into android activity/fragments. Dexter library Writing the code to implement runtime permission in android is a tedious task for developers. Facebook introduced Shimmer library to make loading screen more interesting. You have already seen this in Facebook's mobile apps.