This thesis presents the full-stack development process of TreasureChest, a cross-platform Credential Manager application developed during my internship at Lutech, a company specializing in IT consulting and technology delivery. The name TreasureChest was chosen to emphasize the value of personal information. The application allows users to securely store and easily retrieve their credentials (such as login data for banking services or social networks) without the need to memorize them. Designed to be intuitive and user-friendly, it targets a wide range of users across different age groups. To reach both Android and iOS users, the project was implemented using a cross-platform framework.