Upon further "study" and reading the references Glenn and Jane found, I notice (on more careful inspection) that the "blade" of the thing is most definitely curved... as would be necessary for making barrel staves. So with this blade in place, the contraption would probably be indeed a cooper's bench. Most likely, other blades (or planes) could be substituted for other uses... or with different radial dimensions for making different sized barrels. Most interesting research! [Dan Drew]

A Cooper's bench
[Jane E. Moore]

The Shaving Horse is a simple foot-operated vice that allows you to hold a piece or wood ... relatively easy to build and extremely useful to. [Glenn in ND]