http://www.ebay.com/itm/BRIGGS-STRATTON-5-HP-DUEL-SHAFT-ENGINE-VERY-RARE-/301180363974?pt=LH_DefaultDomain_0&hash=item461fbfa4c6

Its a B&S engine with two different output shafts. I know the smaller one drives at a lower rpm I believe. I was just curious what it would have been used for.

Total SWAG - small riding tractor with mower attachment?

With the speed reducer those shafts come out of it could be used in lots of stuff.

Snow blower comes to mind, one shaft drives the propulsion and the other drives the auger or screw.

Chilly

Looks like a rototiller engine and the extra shaft is for reverse.

Ditto on roto tiller, dual shafts eliminated having any external gearing, just 2 slip belt clutch assemblies, like so:
http://tulsaenginewarehouse.com/catalog/belt_view.jpg

I have one, came off a roto tiller.   I believe the second shaft pulley runs off the camshaft, so half speed.   There was a big push mower that used an engine that ran the whole works off the cam, wonder how they worked out the bearing issue?