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

The Facebook SDK for Android is the easiest way to integrate your Android app with Facebook's platform. The SDK provides support for Login with Facebook authentication, reading and writing to Facebook APIs and support for UI elements such as pickers and dialogs.

The Facebook SDK for Android enables people to sign into your app with Facebook Login. When people log into your app with Facebook they can grant permissions to your app so you can retrieve information or perform actions on Facebook on their behalf.

Deprecated Google Cloud Messaging for Android (GCM) is a service that allows you to send data from your server to your users' Android-powered device, and also to receive messages from devices on the same connection. The GCM service handles all aspects of queueing of messages and delivery to the target Android application running on the target device. GCM is completely free no matter how big your messaging needs are, and there are no quotas.

Make your games social with Google Play game services. Add achievements, leaderboards, real-time multiplayer, and other popular features using the Google Play game services SDK. Let players sign in using their Google+ identities and share their gaming experience with friends. Visit developers.google.com/games/services for more information about integrating game services into your app.

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.

Square helps millions of sellers run their business-from secure credit card processing to point of sale solutions. Get paid faster with Square.

HTTP is the way modern applications network. It’s how we exchange data & media. Doing HTTP efficiently makes your stuff load faster and saves bandwidth. OkHttp is an HTTP client that’s efficient by default: HTTP/2 support allows all requests to the same host to share a socket. Connection pooling reduces request latency (if HTTP/2 isn’t available). Transparent GZIP shrinks download sizes. Response caching avoids the network completely for repeat requests. OkHttp perseveres when the network is troublesome: it will silently recover from common connection problems. If your service has multiple IP addresses OkHttp will attempt alternate addresses if the first connect fails. This is necessary for IPv4+IPv6 and for services hosted in redundant data centers. OkHttp supports modern TLS features (TLS 1.3, ALPN, certificate pinning). It can be configured to fall back for broad connectivity. Using OkHttp is easy. Its request/response API is designed with fluent builders and immutability. It supports both synchronous blocking calls and async calls with callbacks.