I create XML sitemaps using PHP. It would be good if this were possible using Wappler, but I think it would be best if more general functionality were added in relation to this: the ability to read/write files.
If we could write a mixture of dynamic and static content (to include headers etc.) it should be possible to generate any type of text file (csv, xml etc.) in a much more comprehensive way than using the existing export facility, which is easy to use but very limited.
I think this is one of the most important features missing from Wappler. Please consider voting for it here.