[oboizt]

Excel supports task pane and content apps. So for a task pane app like this, it would be possible to make the same app work in both Word and Excel by modifying the "Capabilities" part o the manifest file. All that needs to be added is the following tag: <Capability Name="Workbook"/>

If the user experience is appropriate, then apps typically work very well in both Word and Excel without any changes to the application code.