The wiki page for SML claims it's used by chip manufacturers like ARM, but no citation.
However, languages like Ocaml and F# are direct descendants of ML, and those languages see wider modern adoption. In this sense ML is kind of equivalent to C, and something like Ocaml is kind of equivalent to C++. Haskell is also in the ML family but its laziness and emphasis on purity keeps it a bit separate from its cousins.
In general, FP sees adoption where correctness is of overriding importance -- e.g., Jane Street's use of Ocaml.
However, languages like Ocaml and F# are direct descendants of ML, and those languages see wider modern adoption. In this sense ML is kind of equivalent to C, and something like Ocaml is kind of equivalent to C++. Haskell is also in the ML family but its laziness and emphasis on purity keeps it a bit separate from its cousins.
In general, FP sees adoption where correctness is of overriding importance -- e.g., Jane Street's use of Ocaml.