Esri provides an [ArcGIS Viewer for Flex](http://help.arcgis.com/en/webapps/flexviewer/) as well as an [ArcGIS Viewer for Silverlight](http://www.esri.com/news/releases/11-1qtr/arcgis-viewer-for-microsoft-silverlight-now-available-for-download.html). 

Strangely though, there are [no plans for a similar viewer for Javascript.](http://forums.arcgis.com/threads/14098-Plans-for-ArcGIS-Viewer-for-Java-Script)

**Are there any 3rd parties that have created a "viewer" for javascript?**

Though they are referred to as "viewers", they are actually viewer-builders: they allow administrators to create web applications without writing any code. The javascript viewer blogged about [here](http://blogs.esri.com/Support/blogs/arcgisonline/archive/2010/09/24/new-features-in-arcgis-com-viewer.aspx) does not allow user to choose tools to include in the app, as can be done with the flex and silverlight versions.

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**Update**

I have developed some capabilities that have been packaged as a combination of an SOE and an Add-in for the silverlight viewer. This works great - when the admin builds a viewer application, he can pick my add-in tool from the list and configure it to use the URL of a server where my SOE is installed. However, from what I can tell there are no add-ins for the javascript viewer. Or am I missing something?