A MasTransit developer specializes in using the open-source .NET distributed application framework, MasTransit, to build enterprise-level applications. They work on messaging systems between services and databases, using MasTransit's support for a variety of message queue systems. Their responsibilities include designing, coding, testing, and debugging applications, ensuring system compatibility, and troubleshooting issues. They also handle the integration of new technologies into existing systems, manage data consistency, and ensure the reliability and efficiency of applications. They work closely with other developers and stakeholders to understand requirements and deliver solutions that meet business needs.