How can I get access to the PHP script of websites like Dropbox?
My answer to How can I get access to the PHP script of websites like Dropbox? on Quora
If a website doesn’t deliberately publish its server-side code (some sites like reddit do this, but it’s pretty rare) then you won’t be able to see it. You can search for an open source clone but these will often be pretty low quality—the smartest open source developers tend to work on libraries that solve common problems rather than putting their efforts in to building complete clones of existing sites.
Dropbox in particularly is a poor fit for your question, because a lot of the secret sauce that makes the service work is in the client application that people install on the own devices. This is not the kind of software you would write in PHP.
Dropbox’s functionality is pretty unique, and I would be very surprised if anyone has written a tutorial that was relevant to building your own implementation—there might be academic papers you could dig up though, or conference presentations.