Esri provides an ArcGIS Viewer for Flex as well as an ArcGIS Viewer for Silverlight.
Strangely though, there are no plans for a similar viewer for Javascript.
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 does not allow user to choose tools to include in the app, as can be done with the flex and silverlight versions.
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?