What tools or platforms have you used for testing mobile applications?

The following tools and platforms are often used for testing mobile applications:

• Appium — a cross-platform tool for automating testing of mobile applications on iOS and Android.
• Espresso — a framework from Google for automated testing of Android applications.
• XCUITest — a tool for testing applications on iOS.
• TestFlight — Apple's platform for beta testing iOS applications.
• Firebase Test Lab — a cloud platform for running tests on real devices.
• BrowserStack and Sauce Labs — cloud services for testing on a variety of devices and operating systems.

The choice depends on the testing goals, platform, and automation requirements.