ArcGIS offers APIs for Web application development on various platforms. The links below direct you to documentation and samples for each API. Esri has provided sample servers so you can practice with the APIs before deploying your own ArcGIS Server.
Develop rich Internet applications with ArcGIS services using the Flex™ framework. The API enables creating applications with an intuitive, visually rich and responsive user interface. The ArcGIS API for Flex takes full advantage of the powerful mapping, geocoding, and geoprocessing capabilities of ArcGIS services.
Develop custom applications with ArcGIS Server services using the ArcGIS API for Silverlight or the ArcGIS API for WPF. Both APIs enable you to create highly interactive, visually rich, and expressive applications for both Web and desktop clients.