OCaml is used for Frama-C (static analysis of C), Coq (a proof assistant), Pyre (Python typechecker), Hack (Typed PHP), Mirage (Unikernel, used by Docker for Wi

OCaml is used for Frama-C (static analysis of C), Coq (a proof assistant), Pyre (Python typechecker), Hack (Typed PHP), Mirage (Unikernel, used by Docker for Widnows and Mac), Flow (Javascript typechecker), semgrep. All of these are serious.