A description of the project is well-written and easy to read.

9. StoriesProgressView

Everybody knows Stories which Facebook and Instagram presented on their apps. Here is a library which introduces StoriesProgressView which extends LinearLayout and allows you to add View like below:

The project contains a short but comprehensive README along with sample app.

10. CosmoCalendar

This library is a custom calendar which offers many features and UI modifications like:

changing calendar orientation,

setting custom text colours,

setting selection types and colours,

defining navigation buttons etc.,

many more.

11. Reflow Text Animator

I hope everybody heard about Plaid app. This library developed by Shazam Engineering team, is a

port of Plaid’s ReflowText that allows easily transitioning between sibling TextViews — no matter their size or style.

The library is really easy to use, plug and play!

12. AdaptiveIconPlayground

This is not a library, but a standalone Android app developed by Nick Butcher for experimenting with adaptive icons. According to the README:

This app finds all installed apps supporting an adaptive icon and displays them in a grid. It then allows you to toggle different mask shapes (approximating how the icon might display on different devices) and explore visual effects may be applied. Currently offered:

Layer translation parallax based on scroll

Layer scale parallax based on touch

13. Tivi

Tivi is an application which tracks TV shows and it is connected to Track.tv. It is developed by Chris Banes. The work is still in progress but what is important, it uses the cutting-edge components, libraries and tools which includes: Kotlin, RxJava 2, usage of all of the Architecture Components (Room, LiveData and Lifecycle-components) and usage of dagger-android for dependency injection.

14. RxIdler

This is an IdlingResource for Espresso which wraps an RxJava Scheduler developed by Square Engineering. It supports RxJava 1 and RxJava 2 as well. Happy Instrumentation testing!

15. MRichEditor

This is a rich text editor sample (based on summernote).

It supports many features, including: Bold, Italic, Underline, Strike-through, Headings (1, 2, 3, 4, 5, 6), Paragraph, Quote, (Un)Ordered List, Code, Horizontal Rule, Link, Image, Justify (Center, Fill, Left, Right), Subscript, Superscript, Font Name and Size, Indent, Outdent, Undo / Redo.

In this case you need to base on the sample app, as there is almost no documentation.

16. Android Clean Architecture Boilerplate

This is boilerplate app that shows a clean architecture approach to Android apps developed by Buffer team and Joe Birch.

Reasons for creating this boilerplate:

To experiment with modularisation. To share some approaches to clean architecture. To use as a starting point in future projects where clean architecture feels appropriate.

The project is written 100% in Kotlin with both UI and Unit tests.

It is really well-documented and great for education purposes! 100% recommendation.

17. RxJava2Debug

If you use RxJava, you know that sometimes it is difficult to read exceptions and find an issue in your Rx stream. And this is the reason why this library was created. You can read more about rational in README.

The library offers:

stack trace generation,

stack trace filtering.

18. Resizer

Resizer is a lightweight and easy-to-use Android library for image scaling. It allows you to resize an image file to a smaller or bigger one while keeping the aspect ratio.

The library is inspired by Compressor library.

The library specification:

Minimum SDK: API 21



Default settings:

targetLength: 1080

quality: 80

outputFormat: JPEG

outputDirPath: the external files directory of your app



Supported input formats:

BMP

GIF

JPEG

PNG

WEBP



Supported output formats:

JPEG

PNG

WEBP



Supported quality range: 0~100

The higher value, the better image quality but larger file size

PNG, which is a lossless format, will ignore the quality setting

19. FaceDetector

This library allows you to detect faces in real time on a camera preview. It greatly works with Fotoapparat library, but is supports also other camera libraries and sources.

The usage is simple and the project is quite well documented.

20. RxGps

This is another library from Florent Champigny. It easily finds a current location for us. It is RxJava2 compatible. It also automatically asks for GPS runtime permissions and checks if play services are available for you.

21. MapMe

MapMe is an Android library for working with Maps. MapMe brings the adapter pattern to Maps, simplifying the management of markers and annotations.

MapMe works with Google Maps and Mapbox. README is comprehensive and the library is written in Kotlin.

22. RevelyGradient

This is a library for an easy gradient management.

You can use it in Java or in Kotlin. Documentation is short but enough to start with ease.

23. LiteUtilities

This is a library written in Kotlin, which helps to eliminate boilerplate from your code. Currently it offers:

RecyclerUtils — Remove the need to make an adapter everytime, set up recycler adapter in as little as 4 lines.

ScrollUtils — Easily hide/show FloationActionButton on scroll when using RecyclerView or NestedScrollView.

ToastUtils — Creating toasts are just a function away.

SPUtils — Simple DSL for Shared Preferences.

ValidatorUtils — Fast and simple text validation.

LogUtils — Simple and easy android logging.

24. KOIN

KOIN is a dependency injection framework that uses Kotlin and its functional power to get things done!

According to the author, there is:

No proxy/CGLib,

No code generation,

No introspection

Its documentation is really good, with examples and wiki. There are also contact information (even with Slack).

25. koptional

Minimalistic Optional type for Kotlin that tries to fit its null-safe type system as smooth as possible.

Rationale according to authors:

We don’t think that Kotlin itself needs Optional because it has strong null-safe type system that effectively eliminates need in such a wrapper. However there are APIs and libraries like RxJava 2 which don't accept null values. We also think that in many cases you can use sealed class es to express absent values, however in simple cases like passing String? through Rx stream Optional is a more convenient solution.

For more go to their Github.

26. Parallax

This is an easy parallax View for Android simulating Apple TV App Icons.

README is really good and worthy to check.

27. droid-vizu

Droid-vizu aims to provide customised visualisation effects by easily swapping Renderer to get cool effects

28. Drone

This is not the Android library but a library manager delivered by César Ferreira. It was written due to jealousy of the node.js community for their fast and reliable dependency managers. So instead of googling a library, checking it, reading docs etc., you just do:

drone add creator/library module

For instance:

drone add jakewharton/butterknife

The documentation is really good and this is really worthy to check.

29. From-design-to-Android-part2

This is a project covering creating neat UI on Android. This time, Saúl Molinero covers:

using ShapeShifter tool by Alex Lockwood

AndroidVectorDrawables ,

, ScaleDrawables ,

, Adaptive Icons and more.

It is a truly great lecture!

30. Reagent

Reagent is a Jake Wharton place for experiments for future reactive libraries. Should you use it? No.