SaaS Developer volunteering to implement your idea

A little bit about me: I am primarily a backend developer. I recently learnt a bit of front end programming. I want to do a toy project where I implement both the backend and the front end, end-to-end. Instead of implementing yet another todo application, I thought I would implement a genuine business idea which could be useful for someone. So, if you have a good SaaS business idea/proposal which you wish gets implemented by an engineer, I will be happy to implement it for you. There is no need for you to pay me any money. I will do the code for the API backend, web front end, put the source in a github project, with public domain rights, which you can take and use on your own (for hosting etc.). I will not do any CSS styling though. I will implement the API backend in Scala or Go. The web front end in react+redux. It need not be a pure business idea too, if you wanted something that could help in your day-to-day productivity improvements if a website existed for that, you could send that idea too. Please make sure your idea is explained as elaborate as possible (with screen mockups preferably) as I am not a native english speaker. I provide absolutely no guarantee on the rightness of the system or the timeliness of when the work will be done. At the minimum expect things to take at least a month. Suggestions ?