XNU is described as 'kernel is part of the Darwin operating system for use in OS X and iOS operating systems. XNU is an acronym for XNU is Not Unix' and is an app in the OS & Utilities category. There are four alternatives to XNU for Linux. The best alternative is Linux kernel, which is both free and Open Source. Other great apps like XNU are Linux-libre (Free, Open Source), GNU Hurd (Free, Open Source) and Redox (Free, Open Source).
Linux-libre is a GNU package that is maintained from modified versions of the Linux kernel. The aim of the project is to remove any software that does not include its source code, has its source code obfuscated or released under proprietary licenses.
GNU Hurd (usually referred to as the Hurd) is a computer operating system kernel designed as a replacement for Unix, released as free software under the GNU General Public License. It has been under development since 1990 by the GNU Project of the Free Software Foundation.