When I first worked in Singapore the company wanted to be fully legal. We asked the Thai Embassy for multi-entry B visas for the year ie one page in passport. Many embassies issue these but Singapore Thai Embassy said only single entry. We said feck that. :-) Not using all of our passports up.
B visa is for "Business". Mainly to work in Thailand with a Work Permit. It is also used for business trips to Thailand. People were supposed to get one to attend meetings etc in Thailand as a visitor. The rules were relaxed allowing this on Visa Exempt etc
The "Non" is just for "Non-Immigrant". It says that on O and B visa stamps and I suspect others. It is weird if they were granted that. Dependents of "B" Visa holders get "O" not "B".
Anonymous participant Yes, available at every office I know of. They will come and pick up your passport then return it with the report done. Agents are options for almost everything. 🙂