Allowing anyone to publish a post plugin

You already have the tools for that:

https://www.milliondollaredvertise.com/wp-register.php

To define what newly registered users can do, go to Options > General and set ‘New User Default Role’ to Contributor (can only submit drafts) or Author (draft and publish privileges). I strongly recommend Contributor for new users. You can always reset the role for those you trust.