I recently found Responsively [1], which looks a lot like OP's Sizzy [2], but I doubt it's about those apps, because Sizzy has been shipped for a while now, and

I recently found Responsively [1], which looks a lot like OP's Sizzy [2], but I doubt it's about those apps, because Sizzy has been shipped for a while now, and Responsively is free (Kitze mentions paying in the article). [1] https://github.com/manojVivek/responsively-app https://github.com/manojVivek/responsively-app [2] https://sizzy.app https://sizzy.app