This blue, yellow, and chrome italian bike (BICI DA CORSA MUCELLI) has a 2-cog freewheel (almost like a tandem stoker gear) embedded in the right chainstay, which splits into 2 parallel plates and back at the midpoint.
I can imagine that, although it presently uses the same number (28:28?) of teeth for the 2-speed freewheel, it was probably designed to be used with either a 2:1 or 1:2 gear, maybe 14-28 or 28-14, so that you could have a tremendously low or tremendously high 5-speed geartrain on the bike.
The bike appears to be 52T front and 14-26T in the rear (roughly). That would be a 54-100 gear, in inches. With a change of 'stoker' cogs, you might get 26-50 gear inches, or 108-200 gear inches, and the later would be unheard of, on all but bonneville land-speed record bikes. Those land-speed record bikes have a similar drivetrain, and I have seen them put the reduction gear up by the seat cluster.
- Don Gillies
San Diego, CA, USA