1. PhotoView

 - Use for: For implementing functions such as zooming in and out when viewing pictures

 - License: Apache License 2.0

2. RecyclerView Animators

 - Use for: RecyclerView for dynamic loading and animation

 - License: Apache License 2.0

3. glide

 - Use for: Image Loader

 - License: https://github.com/bumptech/glide/blob/master/LICENSE

4. ImagePicker

 - Use for: for selecting and shooting pictures

 - License: Apache License 2.0

5. CircularImageView

 - Use for: Implement rounded image view

 - License: Apache License 2.0

6. MPAndroidChart

 - Use for: Implement curve, user correct rate, solving speed statistics chart

 - License: Apache License 2.0

7. FloatingActionButtonSpeedDial

 - Use for: Open / Close FAB implementation

 - License: Apache License 2.0

8. MaterialEditText

 - Use for: Implement Material EditTextView

 - License: Apache License 2.0 (included in README.md)

9. SlidingIntroScreen

 - Use for: Implement Sliding Intro Screen

 - License: Apache License 2.0

10. AndroidUtilities

 - Use for: Helper classes to reduce the effort of coding

 - License: Apache License 2.0