The GNU Hurd is the GNU project's replacement for the Unix kernel. It is a collection of servers that run on the Mach microkernel to implement file systems, network protocols, file access control, and other features that are implemented by the Unix kernel or similar kernels (such as Linux).
The kernel is the heart of any operating system. Linux is a free kernel originally created by Linus Torvalds with the assistance of developers around the world. Developed under the GNU General Public License, the source code for Linux is freely available to everyone.
Open source project sponsored by Sun Microsystems, Inc, that is initially based on a subset of the source code for the Solaris Operating System. It is a nexus for a community development effort where developers from Sun and elsewhere can collaborate on developing and improving operating system technology. The OpenSolaris source code will find a variety of uses, including being the basis for future versions of the Solaris OS product, other operating system projects, and third-party products and distributions.