Solaris is one of them, unless you made significant changes to the kernel itself. Darwin, as shipped by Apple is another. There are a variety of embedded OS'

Solaris is one of them, unless you made significant changes to the kernel itself. Darwin, as shipped by Apple is another. There are a variety of embedded OS' that are the same. So yes, as shipped and delivered, you can't replace the standard library and the vendors both consider the standard library as part of the OS. And furthermore, existing application binaries for those platforms would not work without them.