Vietnam
I frequently travel alone to Vietnam (Ho Chi Minh City) on business and it is a safe country (subject to the usual sensible precautions). The most dangerous thing in Ho Chi Minh City (Saigon) is the traffic as there are so many motorcycles and zebra crossings don't mean anything. When you want ot cross you have to walk at a steady pace and the bikes will find their way around you - problems really only arise if you suddenly stop.
I eat in restaurants on my own and have no problems, similarly walking back to my hotel at night.
I haven't yet been to the rest of the country but I cna't see it woudl be any different.
The Vietnamese people are lovely.