I have my finished prototype, but what files do I send along? Assets is an obvious one but what about ProjectSettings or Library?

(it's a Unity project if it helps)

Then, duplicate the folder(unless you don't want to keep a copy), and open it. Inside, you should see things like "Library". Remove everything except the folders titled

"Assets", "Packages", "Project Settings", and "User Settings".

The libraries is what you REALLY want to destroy, as it is several GB.

Could you post a link to your game please? I really want to see it.