About GC and real-time constraints, I’d guess that Jane Street, at least, has some applications where response times are important. I think I remember reading a remark by @Yaron_Minsky that JS likes OCaml partly because of the control that GC tuning parameters gives them, but I can’t find it now. And there has been relatively recent work on improving latency in the OCaml GC, apparently partly in response to Jane Street’s interest:
None of this conflicts with points @perry, @smolkaj, and @darrenldl made about memory management and Rust (a language I know almost nothing about, anyway).