Joe Otterson TV ReporterThe “Stranger Things” universe is expanding at Netflix, with the Duffer Brothers lining up multiple projects within the world they created for the series.Under their overall deal with Netflix, the Duffers — Matt and Ross — have established the production company Upside Down Pictures, bringing on Hilary Leavitt to run the company.Among the new projects they have in development, the Duffers are officially working on a “Stranger Things” spinoff series, though exact plot details remain under wraps. The show will be based on an original idea by the Duffers with Upside Down Pictures and 21 Laps producing.