A Gemfury developer manages private package repositories for various programming languages. They work on creating, storing, and sharing private or public packages in a secure and reliable manner. Their tasks include uploading and installing packages, managing package versions, and controlling access to these packages. They work with languages like Ruby, Python, JavaScript, PHP, and others. They also ensure the smooth integration of Gemfury with existing developer workflows and tools, such as Github, Bitbucket, or GitLab. In addition, they troubleshoot any issues related to package deployment and ensure optimal performance of the Gemfury platform.