Welcome to the OpenELEC WIKI
Since the Gotham builds of OpenELEC (version 4.x), the number of OpenELEC builds for specific hardware has been reduced. The Generic build (64 or 32bit) now supports Nvidia, AMD, and Intel based graphics. There are still specific builds for AppleTV (1st gen) and Raspberry Pi.
OpenELEC is ideal for smaller systems as the lightweight footprint means that your machine's resources aren't wasted on the operating system. Additionally, support for NVIDIA's VDPAU, AMD's XVBA, Intel's VAAPI and Broadcom's Crystal HD chip means that high-definition content can be offloaded to supported graphics cards to allow low powered systems based on Intel's Atom or AMDs Fusion processor to be effectively used as a media center base.
Unlike other XBMC distributions, OpenELEC isn't based on Ubuntu, Debian or Arch - in fact, it's not based on any distribution. Instead, OpenELEC has been built from scratch specifically to act as a media center. This means it can be streamlined to certain hardware and only needs to include the packages absolutely required, making OpenELEC as streamlined as possible. In addition, OpenELEC is designed to be managed as an appliance - it can automatically update itself, is managed almost entirely from within XBMC and boots in seconds. You never need to see a management console or have Linux knowledge to use it.