High Quality Content by WIKIPEDIA articles! Microsoft Windows Services for UNIX or Subsystem for UNIX-based Applications is a software package produced by Microsoft which provides a Unix subsystem and other parts of a full Unix environment on Windows NT and its successors. The subsystem included is called Interix. These are available free from Microsoft as a download or as part of the Windows OS distribution. Like the Microsoft POSIX subsystem in Windows NT that it replaces, Interix is not an emulation of a Unix kernel, but rather an implementation of a user-mode subsystem running directly on top of the Windows NT kernel.