What are the types of WebDriver APIs available in Selenium?

System.setProperty("webdriver.gecko.driver", "path/to/geckodriver");
WebDriver driver = new FirefoxDriver();

System.setProperty("webdriver.chrome.driver", "path/to/chromedriver");
WebDriver driver = new ChromeDriver();

System.setProperty("webdriver.ie.driver", "path/to/IEDriverServer.exe");
WebDriver driver = new InternetExplorerDriver();

System.setProperty("webdriver.edge.driver", "path/to/msedgedriver");
WebDriver driver = new EdgeDriver();

// No System.setProperty needed on Mac
WebDriver driver = new SafariDriver();

WebDriver driver = new HtmlUnitDriver();  // No browser UI
// Fastest implementation — runs in memory, no browser window

OperaOptions options = new OperaOptions();
options.setBinary("/path/to/opera");
WebDriver driver = new ChromeDriver(options);  // Opera uses Chromium engine

WebDriver driver = new RemoteWebDriver(
    new URL("http://localhost:4444/wd/hub"),
    new ChromeOptions()
);

// For mobile browser automation
DesiredCapabilities caps = new DesiredCapabilities();
caps.setCapability("platformName", "Android");
WebDriver driver = new AndroidDriver(new URL("http://localhost:4723"), caps);

// No need to set system property manually
WebDriverManager.chromedriver().setup();
WebDriver driver = new ChromeDriver();