@Robert *******
they are both non-immigrant visas. That's what "non" means. Non-O is "Other" and covers many things like retirement, marriage, volunteer, etc. But it's a 90 day visa.
The non-OA is also a non-immigrant visa but it has much higher requirements and is a 1-year multiple entry visa.
Most people want the non-O as they don't want the insurance requirement.