1. 1. Scalability: ActiveMQ is a message-oriented middleware that is built on the Java Message Service (JMS) standard, which allows for high scalability and distributed messaging. It can handle very large message volumes and can be easily scaled up to meet the demands of a growing system. On the other hand, Protobuf is not specifically designed for scaled message distribution but rather focuses on efficient serialization and deserialization of structured data.
2. 2. Language Support: ActiveMQ primarily supports Java, but it also provides support for multiple languages through connectors and protocols. It can be used with languages such as C++, .NET, Ruby, and more. On the other hand, Protobuf is a language-agnostic data serialization format that can be used with various programming languages, including Java, C++, Python, and more. It provides APIs for generating code bindings in different languages.
3. 3. Message Format: ActiveMQ supports various message formats, including TextMessage, BytesMessage, ObjectMessage, and MapMessage. These formats allow flexibility in exchanging different types of data between systems. In contrast, Protobuf uses a binary message format that optimizes data serialization for efficient storage and transmission. It uses a structured schema definition to define the message format and provides efficient serialization and deserialization of the data.
4. 4. Persistence: ActiveMQ provides built-in persistence options like JDBC, KahaDB, and LevelDB, which allow messages to be stored in databases or disk-based stores. This ensures message durability and reliability even in the event of system failures. On the other hand, Protobuf does not have built-in persistence capabilities as it focuses on efficient data serialization, and it's up to the application to handle persistence if required.
5. 5. Messaging Patterns: ActiveMQ supports a wide range of messaging patterns, including point-to-point, publish/subscribe, request/reply, and more. These patterns enable different communication styles between applications and components. In contrast, Protobuf does not provide native support for messaging patterns as it is primarily focused on the serialization and deserialization of structured data.
6. 6. Interoperability: ActiveMQ provides seamless integration with other JMS-compliant messaging systems, allowing for interoperability between different messaging implementations. It can ensure compatibility and communication between systems using different messaging platforms. Protobuf, on the other hand, can be integrated into various systems and languages through code generation, enabling interoperability at the data level.

In Summary, ActiveMQ offers scalability, language support, various message formats, persistence options, messaging patterns, and interoperability, making it a powerful message-oriented middleware. Protobuf, on the other hand, focuses on efficient data serialization and does not provide native support for messaging patterns or built-in persistence.