The kernel runs on Intel and Alpha hardware in the general release, with SPARC, PowerPC, MIPS, ARM, Amiga, Atari, and SGI in active development. The SPARC, PowerPC, ARM, PowerMAC - OSF, and 68k ports all support shells, X and networking. The Intel and SPARC versions have reliable symmetric multiprocessing.
Work on the kernel is coordinated by Linus Torvalds, who holds the copyright on a large part of it. The rest of the copyright is held by a large number of other contributors (or their employers). Regardless of the copyright ownerships, the kernel as a whole is available under the GNU General Public License. The GNU project supports Linux as its kernel until the research Hurd kernel is completed.
This kernel would be no use without application programs. The GNU project has provided large numbers of quality tools, and together with other public domain software it is a rich Unix environment. A compilation of the Linux kernel and these tools is known as a Linux distribution. Compatibility modules and/or emulators exist for dozens of other computing environments.
The kernel version numbers are significant: the odd numbered series (e.g. 1.3.xx) is the development (or beta) kernel which evolves very quickly. Stable (or release) kernels have even major version numbers (e.g. 1.2.xx).
There is a lot of commercial support for and use of Linux, both by hardware companies such as Digital, IBM, and Apple and numerous smaller network and integration specialists. There are many commercially supported distributions which are generally entirely under the GPL. At least one distribution vendor guarantees Posix compliance. Linux is particularly popular for Internet Service Providers, and there are ports to both parallel supercomputers and embedded microcontrollers. Debian is one popular open source distribution.
The pronunciation of "Linux" has been a matter of much debate. Many, including Torvalds, insist on the short I pronunciation /li'nuks/ because "Linus" has an /ee/ sound in Swedish (Linus's family is part of Finland's 6% ethnic-Swedish minority) and Linus considers English short /i/ to be closer to /ee/ than English long /i:/ dipthong. This is consistent with the short I in words like "linen". This doesn't stop others demanding a long I /li:'nuks/ following the english pronunciation of "Linus" and "minus". Others say /li'niks/ following Minix, which Torvalds was working on before Linux.
More on pronunciation (//foldoc.org/pub/misc/linux-pronunciation).