AppMon is an automated framework designed for monitoring and tampering with system API calls of native applications across macOS, iOS, and Android platforms. The framework is built on Frida and provides several specialized components for different security testing scenarios. The AppMon Sniffer component enables security researchers to intercept and analyze API calls made by applications during runtime. AppMon Intruder allows for real-time manipulation of data flowing through these API calls, facilitating dynamic analysis and security testing. For Android applications, the framework includes AppMon Android Tracer, which specifically focuses on tracing Java classes within Android APK files. The AppMon IPA Installer component extends functionality to non-jailbroken iOS devices, while AppMon APK Builder works with non-rooted Android devices. The framework supports cross-platform mobile application security testing and provides capabilities for both static and dynamic analysis of mobile applications. It includes documentation and experimental features for advanced security testing scenarios.