A developer shares their experience building a simple fitness tracker app using the Python library Reflex, which facilitates the creation of reactive applications through a functional and declarative approach. The app focuses on logging weekly workout completions, utilizing Reflex's integration with sqlmodel for database interactions. The process begins with setting up a project environment using the uv tool, followed by configuring Reflex with a SQLite database. The app's architecture includes a State class to manage backend data and methods and an index function to define the user interface. Key features like weekly progress tracking, workout logging, and navigation through past and future weeks are implemented. The article highlights the developer's approach to learning Reflex through experimentation and documentation review, noting the framework's promising capabilities for quickly developing customizable web applications. The author expresses excitement about Reflex's potential compared to other tools like Streamlit, while also acknowledging the need for more robust solutions like Django for complex projects.