This is Moscow ML, a version of Standard ML:

The current version 1.43 of Moscow ML
    * implements the Core language of Standard ML, as revised 1996
    * implements large parts of the new SML Basis Library
    * implements separate compilation and a limited version of the
      Standard ML Modules language, with signatures and structures
      but no functors
    * can produce compact stand-alone executables (a la Caml Light)
    * supports quotations and antiquotations, useful for metaprogramming
    * includes several new libraries and a new type `char'

Homepage:
https://mosml.org/
