I don't know how complete it is, but NonStop has had POSIX support since the mid-1990s. It's called Open System Services. It's got ksh, and various unix/posix a

I don't know how complete it is, but NonStop has had POSIX support since the mid-1990s. It's called Open System Services. It's got ksh, and various unix/posix apis/utilities, and a hierarchical filesystem.