The great majority of websites, though, DON'T need a mobile app; they need a website that works on mobile. Most smartphone users are unwilling to download more than a few apps for websites, anyway; if your website is a restaurant, a news source, or anything else that works well on a website, most users are unwilling to download and install your app anyway. So, if you want their business, you need to make your website work for mobile. Once you have done, that, in most (not all) cases, you don't need to develop an app anyway.

unless you use Turbolinks with IOS/Android adapters or another hybrid app alternative