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

Volley is an HTTP library that makes networking for Android apps easier and most importantly, faster.

Bolts is a collection of low-level libraries designed to make developing mobile apps easier. Bolts was designed by Parse and Facebook for our own internal use, and we have decided to open source these libraries to make them available to others. Using these libraries does not require using any Parse services.

Crashlytics helps collecting, analyzing and organizing app crash reports

An image loading and caching library for Android focused on smooth scrolling. Glide is a fast and efficient open source media management and image loading framework for Android that wraps media decoding, memory and disk caching, and resource pooling into a simple and easy to use interface.

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.

Okio is a new library that complements java.io and java.nio to make it much easier to access, store, and process your data.A modern I/O library for Android, Kotlin, and Java

Retrofit is type-safe REST client for Android and Java which aims to make it easier to consume RESTful web services. ... Retrofit automatically serialises the JSON response using a POJO(Plain Old Java Object) which must be defined in advanced for the JSON Structure.

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.