> What should a developer do that needs to share state across a Forgo app?

We already have many facilities in JS to handle state. Singleton patterns, closures etc. The example on the website uses closures to handle component state - which is simpler than React's hooks based approach.

  function SimpleTimer() {
    let seconds = 0; // Just a plain variable

    return {
      render(props, args) {
        setTimeout(() => {
          seconds++;
          rerender(args.element); // rerender!
        }, 1000);
  
        return <div>{seconds} secs have elapsed...</div>;
      },
    };
  }

> I don't consider reducers, actions, redux/flux to be React specific

They didn't emerge from React - but it isn't possible to do React without them. When I conduct trainings, I often see some of my students go - wow, why would you do that? So Forgo basically is an exploration of how to simplify things - and to let users pick their desired level of complexity.