MongoDB and MySQL are two popular open-source database management systems that cater to different needs. MongoDB is designed for scalability, high performance, and flexibility in handling large volumes of unstructured or semi-structured data, making it suitable for modern web applications, big data projects, and real-time analytics. Its schema-less design allows for rapid iteration and scalability, whereas MySQL organizes data into tables composed of rows and columns, ideal for structured data and complex queries. MySQL provides full ACID compliance, ensuring the data remains consistent and accurate, while MongoDB follows a BASE model prioritizing availability and partition tolerance over strict consistency. MongoDB is better suited for applications requiring flexible data models, rapid iteration, and high performance, whereas MySQL excels in handling structured data, complex joins, and financial transactions. Both databases offer open-source licenses, cloud-native application support, and programming language support, making them versatile choices depending on specific requirements.