The Kernel and the Distro
The Linux kernel powers many operating system, most of which use the basic GNU userland utils, which are commonly known as GNU/Linux operating systems.
Since the beginning of the 90's, GNU/Linux distributions are UNIX-like operating systems which have found their way into the data center, in many cases replacing Windows or proprietary UNIX solutions. One of GNU/Linux best qualities is probably the ecosystems built around it. There are plenty of distributions specifically targeted at different client needs: from desktops to data center servers, there will probably be a GNU/Linux distribution tailored for you.
Software Ports
GNU/Linux distributions aren't just an Operating System. Distribution are often built with the help of the community and, such as Debian does, have software repositories full of pre-built and ready to install packages for your distribution of choice. Currently, major GNU/Linux distributions' software repositories host more than 20.000 prebuilt software packages.
The Linux Kernel is Open Source
The Linux Kernel Project caught people's attention back in the 90's, and nowadays still is one of the best known Open Source projects out there actively maintained. Having access to full kernel source code gives you the possibility of inspecting, assessing and even modify and rebuild the kernel yourself.
Whether you're using GNU/Linux as a platform for your applications or you're developing sophisticated solutions on top of your own kernel, from the veteran Slackware, the ubiquitous Debian and Ubuntu based distributions, up to enterprise-level Red Hat's Enterprise Linux and Novell's SUSE, Reacts has the knowledge to assess and help you build your GNU/Linux data center.
Platforms
GNU/Linux distributions are available for a myriad of platform, including x86, ia64, AMD64, SPARC.