Saving a website that is already published

I know similar questions have been asked but it still does not seem possible. Having spent ages getting a website 'just right' online is there a way to save it as a project or template for future use in another website? It seems ridiculous having to start from the beginning each time.
Is the only solution to achieving this the download of a plugin? almost everyone needs this ability so can you tell me if it's possible and explain the process please.
Thank you