A Lync Server developer designs, develops, and maintains communication solutions on the Lync platform. They create applications to integrate with Lync Server, enhancing its capabilities. They use APIs like UCMA, UCWA, and Lync SDK to develop video, voice, instant messaging, and conferencing features. They also ensure system stability, security, and performance by managing, troubleshooting, and upgrading the Lync Server. Furthermore, they work on integrating Lync with other Microsoft products like Exchange and SharePoint. Their job involves a deep understanding of the Lync architecture, .NET development, and unified communications technologies.