That’s pretty much what I wanted ask right there. 
What’s the stuff they have in little brown bottles at Chinese food places? Liquid MSG? Or is it soy sauce…whichever it is, it tastes very salty.
A salt substitute that tastes like salt?
Yes. It’s called salt.
There are plenty of non-sodium-chloride salts out there that taste salty, but they’re still salts.
So if you don’t want sodium chloride (NaCl) you could get something like potassium chloride (KCl). Of course, then you’re getting lots of potassium. You can use Bragg’s liquid aminos instead of soy sauce; they’re a soy-based sauce, high in protein and amino acids without the heart-stopping volume of sodium. But realize that KCl is still a salt. It’s not “salt” as you think of it, but it’s still a salt. Likewise, that soy-based sauce still contains salts which (surprise) are what makes it taste salty.
The most common reason a person will have for using salt substitutes is that they have salt (sodium, actually) sensitive hypertension (blood pressure). For such people, potassium chloride is a perfectly acceptable substitute, and very few (if any) people have any reason to avoid potassium.
Usually, when people say they want to avoid salt, they mean that they want to avoid sodium. Soy sauce is loaded with salt, and MSG is loaded with sodium. Neither is good for someone on a low salt diet.
I’ve never found a really acceptable salt substitute. My mother swears by Mrs. Dash, which is a blend of various herbs and spices. This isn’t a salt substitute, really, but another way of seasoning food. There’s a lot of pepper in all of the Mrs. Dash mixes, so I can’t eat it (pepper and any raw member of the onion family will upset my stomach something horrid), but it’s really a pretty good way to spice up your food, if you can tolerate black pepper and garlic. Sometimes I will make garlic and herb bread, and use Mrs. Dash and garlic on it, and just suffer the consequences, because it’s so tasty.
Some people like the “Lite Salt” seasoning that’s available. Most of these are basically mixes of sodium chloride and potassium chloride. As I said, I don’t consider this stuff a good salt substitute, but some people like it. Or at least can stand it.