The Otis Elevating Railway as it was 6'4" between the outer rails of the 3 rail line. After it was rebuilt, it handled and interchanged cars between the Catskill Mountain Railroad at the lower end and Catskill & Tannerville Railroad at the upper connection. Both of these were very truly narrow gauge at 3'.
More interesting was the brake systems used on some of the cars that were interchanged. They were equipted with automatic air brakes plus vacuum brakes and also had hook loops on the side of the cars so they could be pulled by a cable off the incline onto the C&TRR.