React Native and Expo's cross-platform capabilities, combined with Clerk's user management and Supabase's backend, offer a comprehensive toolkit for developing production-ready mobile applications. This guide provides a detailed walkthrough on building a time tracking app named Aika from scratch, utilizing React Native and Expo for the interface, Clerk for secure authentication, and Supabase for data storage. Clerk simplifies secure user management by offering session handling and multiple authentication methods, including email/password and OAuth. Supabase, an open-source Firebase alternative, provides a PostgreSQL database with simple API access, supporting seamless integration with Clerk for enhanced security and scalability. The tutorial outlines the implementation of key app features such as a timer, authentication, user settings, and data management, culminating in a fully functional, cross-platform app that operates on both iOS and Android. Additionally, the guide highlights the benefits of using these tools to streamline development processes and ensure robust security practices, with a promise of further enhancement in future articles through Clerk's multi-tenancy features for team collaboration.