SML# is one of the lesser known SML implementations, although it's a quite good one. The only thing that I found impractical,... you can only link 32bit libs, which is very odd on todays 64bit Systems.

Nevertheless, the thing I like most at SML# is the excellent FFI. You can just pass SML-records or SML-functions to C. SML# is very powerful if you code your applications in SML and C.