MicroPinner is a lightweight dialog-only application, that turns your statusbar into a pingboard. (You can basically create your own notifications)
You can customize the notifications title and content, as well as its priority and visibility (Works on Android 5+ only).
java-object-diff is a simple, yet powerful library to find differences between Java objects. It takes two objects and generates a tree structure that represents any differences between the objects and their children. This tree can then be traversed to extract more information or apply changes to the underlying data structures.
Defrag is a simple to use library that allows for Fragment-free Android applications.