An ArcEngine developer utilizes Esri's ArcGIS Engine to create custom geographic information system (GIS) applications. They integrate and deploy GIS functionality such as mapping, geocoding, routing, and geoprocessing into standalone applications. They write code to manipulate data, perform analysis, and visualize results in a geographic context. They often work with other programming languages like Python, Java, or .NET to extend the capabilities of the GIS software. These developers also ensure the GIS applications are properly integrated with databases, servers, and other systems. They troubleshoot issues, optimize performance, and may also provide user support and training.