The ArcGIS Web APIs offer similar GIS functionality; you choose your preferred developer platform.
Each API provides the resources you need. Read the API reference; view working samples that help you get started and show you what's possible; and communicate with others through the forums, blogs, and code galleries.
Develop custom 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.