The Manhattan Firearms Manufacturing Co. was incorporated in (surprise!) Manhattan, but their manufacturing facilities were first in Norwich, CT and later in Newark, NJ. Their first products were single shot percussion pistols, followed by pepperbox revolvers (several barrels turning like a revolver cylinder).
After Colt's patents expired, Manhattan made a series of percussion revolvers in .31 and .36 caliber, nearly identical in appearance and size to the Colt revolvers in the same calibers. AFAIK, they never made a .44 caliber.
One characteristic of the Manhattan revolvers is the extra cylinder notches (12 in the case of a 6-shot cylinder) to provide a means of safe carry. With the cylinder stop locked into the safety notch, the hammer was between caps and the gun could not fire if dropped. (Colt used a safety pin in the cylinder over which a notch in the hammer nose fitted for the same purpose.)
Later, Manhattan made .22 caliber "tip-up" revolvers very similar to those made by S&W. They also made, quite late, a screw barrel percussion pistol.
Jim