Originally Posted by Jeff Wills

Agreed. It looks like it's an old SunTour cassette hub to me. It'll take two chainwhips and a lot of force to loosen the small cog, assuming it's not rusted in place.

Is there some reason you want to save it? SunTour cassettes haven't been made in nearly 20 years, and they're the only cassette that fits that hub. 100% incompatible with Shimano or clones.