You said:
"So what is the difference between a class boat and a fomrula boat (A class versus formula 16) and what is the definition of: Open Class; One design; Development Class"

Class boat, roughly equivalent to one design:
Usually same manufacturer, (can be more than one) strict rules as to sail, hull, spars configurations, must be identical, or as identical as possible (identical=onedesign). Hobie 16, Tornado, J-boats are onedesign.

Formula boat:
Can be by many different manufacturers, the rule here is conformation to a 'formula' which defines sail area, waterline length, and overall boat weight. Within those parameters and a few more, you can do whatever you want. America's Cup boats are formula boats, as are the NACRA F18, Hobie Tiger, etc. I would call the Acat more of a formula boat than a true 'class' boat.

Open class:
Racing whatever type of boat you like, scoring is equalised by assigned handicap numbers, such as Portsmouth, PHRF, or Texel, etc.;

Development class:
Similar to formula, but with fewer rules as to boat configuration, and more open as to modification. Usually sail area and waterline length are the only restrictions. In the case of the 18 Square, for example, the class is divided by weight into categories, but the division is broad. The 18 Square is a development class boat, as are the C-cats.

Hope this is a bit more clear,
sea ya
tami