The Android platform provides a framework API that applications can use to interact with the underlying Android system. The framework API consists of: A core set of packages and classes. A set of permissions that applications can request, as well as permission enforcements included in the system

Firebase is a platform developed by Google for creating mobile and web applications

Flutter is an open-source UI software development kit created by Google. It is used to develop applications for Android, iOS, Linux, Mac, Windows, Google Fuchsia, and the web from a single codebase.

Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Gson can work with arbitrary Java objects including pre-existing objects that you do not have source-code of.

The location APIs make it easy for you to build location-aware applications, without needing to focus on the details of the underlying location technology. They also let you minimize power consumption by using all of the capabilities of the device hardware.

Allow your users explore the world with rich maps provided by Google. Identify locations with custom markers, augment the map data with image overlays, embed one or more maps as fragments, and much more.

Google Play services powers a broad set of SDKs on Android to help you build your app, enhance privacy and security, engage users, and grow your business. These SDKs are unique in that they only require a thin client library to be included in your app, as shown in figure 1. At runtime, the client library communicates with the bulk of the SDK's implementation and footprint in Google Play services.

Google Sign-In is a secure authentication system that reduces the burden of login for your users, by enabling them to sign in with their Google Account—the same account they already use with Gmail, Play, Google+, and other Google services. Google Sign-In is also your gateway to connecting with Google’s users and services in a secure manner. You can give your users the opportunity to pay with Google Pay, share with their Google-wide contacts, save a file to Drive, add an event to Calendar, and more. Integrate Google’s user-centric APIs and services inside your app to help your users take action and convert.

A software library that provides scanning features such as barcodes or face analysis to recognize faces in pictures and details about the face as well.

OneSignal is a multi-platform push notification service and it is totally FREE to use. ... Multi-platform support: provides a single UI and API to deliver messages across various platforms such as iOS, Android, Amazon Fire, Windows Phone, Chrome Apps, and so on.