Appium is a free and open source UI testing framework for mobile applications.

The capabilities of Appium are

Test Web supports the JSON wire protocol and is cross-platform for native and hybrid mobile automation.
It does not necessitate recompilation of App Support automation tests on physical devices, similar devices, or emulators. It is not mobile device dependent.

Pre-requisite to use APPIUM is

ANDROID SDK
JDK
TestNG
Eclipse
Selenium Server JAR
Webdriver Language Binding Library
APPIUM for Windows
APK App Info On Google Play
js

Appium does not support Android versions lower than 4.2 for testing.
Support for hybrid app testing is limited. For example, testing the switching action of an application from a web app to a native app and vice versa is not possible.
Appium Inspector is not supported on Microsoft Windows.

To discover the DOM element in an Android application, utilise “UIAutomateviewer.”

Appium is a Node.js-based “HTTP Server” that uses the Webdriver JSON wire protocol to drive iOS and Android sessions. As a result, Node.js must be installed on the machine before the Appium Server can be started.
When we download and install Appium, it creates a server on our PC that exposes a REST API.
It receives the client’s connection and command requests and executes them on mobile devices (Android / iOS). It then answers with HTTP responses. Again, the mobile test automation frameworks are used to drive the user interface of the apps in order to carry out this request.

Any language that supports HTTP requests, such as Java, JavaScript with Node.js, Python, Ruby, PHP, Perl, and others, is supported by Appium.

Pros:
Regardless of the platform a programmer is automating (Android or iOS), all of the intricacies will be managed by a single Appium server.
It paves the way for cross-platform mobile testing, which means the same test may be run on various platforms at the same time.
To make your app automation friendly, Appium does not require any additional components.
Cons:
Appium allows you to run scripts on several iOS simulators at the same time.
It uses UIAutomator for Android Automation, which only supports Android SDK platforms with API 16 or higher, and they have used another free source library called Selendroid to handle previous APIs.

Appium offers a “Inspector” to record and playback, similar to Selenium IDE’s record and playback facility. It inspects the DOM to record and play native application behaviour and provides test scripts in any preferred language. Appium Inspector, on the other hand, does not support Windows and instead uses the UIAutomator viewer as an option.

No, you do not require a server machine to execute Appium tests. Appium allows for a two-tier design, in which a test machine connects to a test server that runs Appium, automating the entire process. Appium can be installed on the same computer as your tests.

Yes, you can interact with the App while using Javascript. The server will deliver the script to your app wrapped in an anonymous function to be executed when the commands run on Appium.

Yes, you can run the test in a multithreaded environment, but you must verify that no more than one test is running against the same Appium server at the same time.