That's a SBP shiftkit second edition (they're on their third now) to a
Sturmey Archer XL-RD3 on a 1943 Rollfast & at the time of that pic it had over 4500 miles on it.
As BigBlue linked to, it's a kit & the front sprockets are mounted to a (unidirectional) freewheel bearing on the pedal crank, so you needn't pedal along with the motor.
TBH, I do like the shiftkit & while I don't think I'd build another w/o one - that front freewheel bearing has proved somewhat problematic in the long run. I've destroyed three of them at this point (two cheapos and a quality) no matter the care & maintenance... remembering ofc the thousands of miles I got from them.
The additional maintenance requirements are not insignificant, with three chains just for the drive tensioning and adjustment becomes comparatively constant, not the easiest task as it's not well suited for it, the additional complexity something to be considered for a first time builder.
The Sturmey Archer XL-RD3 on the other hand has performed absolutely flawlessly as has it's mate, the front dynamo hub with 70mm drum brake
Sturmey Archer X-FDD though I would recommend the
XL-FDD for it's larger 90mm drum brake and greater stopping power.
Incidentally, the bike pictured can be found here;
The Rustoration Build Off
Rollfast Photo Album
