A Frege developer is responsible for writing, testing, and maintaining code in Frege, a purely functional programming language similar to Haskell but for the Java Virtual Machine (JVM). They utilize Frege's strong static typing and lazy evaluation to build reliable, efficient, and concurrent applications. They work on integrating Frege code with Java libraries and frameworks, allowing for a seamless blend of functional and object-oriented programming. Frege developers also engage in debugging and problem-solving, striving to optimize code performance and maintainability. They also collaborate with other team members and participate in code reviews to ensure high-quality software solutions.