One Day the World Ended is designed to be an open source and collaborative work of fiction. Most of this will come later when I have more material ready, but the code of the website is on GitHub and you're more than free to issue pull requests if you want to.
At the moment there's one part of the work where you can contribute and I welcome your ideas, this is for the "What happens next" section of the introduction. This is a list of ideas about Worlds that replace our old one after its end. I will accept all reasonable and non-spam ideas and attempt to write a story based on your idea at some point in the future.
If you're technically minded you can create a pull request against this page. If not, but you are happy to create a GitHub account, you can directly edit the page here and that will create a version of the page with your idea that I can consider. If you have an idea, but all of this makes no sense whatsoever, then connect with me and I will also consider your suggestion.