Appium is an open-source tool for controlling native, hybrid, or mobile apps on iOS mobile, Android mobile, and Windows desktop platforms. It allows testers and developers to create automated tests of mobile applications, helping them deliver quality software faster with less risk. Appium has a client/server architecture, communicating with a simple protocol similar to browsers and web servers. The tool supports various programming languages, including Java, JavaScript, C#, PHP, Python, and Ruby. Users can write cross-platform automation code without significant extra effort, isolated from device-specific protocols. Appium can connect to existing physical or virtual devices, or start new virtual devices on demand. It also supports testing Web and Native iOS apps using the XCUITest protocol, as well as automating mobile versions of Safari. Additionally, Appium has numerous capabilities that allow users to configure device settings, such as platform name, app activity, and language. The tool is compatible with various operating systems, including Windows, Mac OS X, and Linux. It also supports Sauce Labs' test cloud and has a free guided bootcamp for learning how to use it.