Business rule to download file

Sorry for being that guy, but why would you need that? Users can download files from the File Explorer on their own, which they will have to do - since you cannot know in advance where, on their local machine, they'll be able to save it...

If you want to have a button in a dashboard that pushes a file down to the user, try the Navigation action, it has an option to navigate to a file.

If you want something to run in the background to export stuff, save the output to the FileSystem Share which is on the server - that's easy to do with a rule.