As mentioned, most of the substitutes described are simply salt-laden, either in their formulation/packing or naturally in the case of cheeses.

I find the "fish sauces" (Nam Pla, etc.) to be addictive and interesting in a variety of dishes, not just seafood, although many are put off by the fishy aroma and taste. But, like anchovies, they get their salty punch from plain old salt (and, let's face it, almost all salt is "sea salt", the only difference being the time away from the sea).