[platz]

F# doesn't even have modules; although it's derived from an ML, it has cut out rather important parts of it to make it fit into the .net ecosystem.

[brandonbloom]

You're not wrong, but I may phrase it differently...

F# lacks modules, instead favoring objects. Although it's derived from OCaml, it has omitted complex features which don't fit in to the .net ecosystem.

[riffraff]

but is there say, something that (S)ML's modules allow which is not possible to do with F#+.NET objects?

I.e. ML's modules can be used to create interfaces and implementations of ADTs, but so can OO interfaces and classes.