The dirtyburger app is actually for the mobile and not on linux using php. For a similar app on mobile, there is further expenses, like the Apple AppStore licences, and Windows App Licences. For Android, since Google is very lenient, it should not be an issue. Apple will reject any application that seems to be the same nature as another one. So similar to dirtybugger would get rejected from Apple immediately.
On the other hand, if you just need a scalable web application which works on all platforms, from desktop to mobile and tablets, which will be open to all and no need to download and install, then it could be built with just PHP and a Database backend. "App for Scale" is easy to say, but the costs that may indulge in the future should be known before. We build apps on top of the AWS Cloud with max scale built in, but that is not PHP/Linux, it is built using Javascript, NodeJS and DynamoDB and uses distributed messages and queues.
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