By the mid-1990s, work on microkernel systems was largely stagnant, although the market had generally believed that all modern operating systems would be microkernel based by the 1990s. The primary remaining widespread uses of the Mach kernel are Apple's macOS and its sibling iOS, which run atop a heavily modified hybrid Open Software Foundation Mach Kernel (OSFMK 7.3) called "XNU" also used in OSF/1. In XNU, the file systems, networking stacks, and process and memory management functions are implemented in the kernel; and file system, networking, and some process and memory management functions are invoked from user mode via ordinary system calls rather than message passing; XNU's Mach messages are used for communication between user-mode processes, and for some requests from user-mode code to the kernel and from the kernel to user-mode servers.