In Beijing, on two occasions, I was served a sauce I couldn't identify.
Visually it looks like soy sauce but it's much thicker and stickier. It tastes soy-ish, but sweeter, maybe malty in some way. Definitely has fermented aspects. I asked someone who lives elsewhere in Asia and he said "sweet sauce" which isn't helpful. During the dinner where I took this picture, I asked my "handler" who said "we just call it sauce" which again wasn't helpful.
Does it have a name outside China? Is this something I could buy, as you can buy oyster sauce, hoisin sauce etc, if only I knew its name? It was really good.