Backdrop CMS is the Drupal fork. It is a faster and less-complex version of Drupal 7 with many of the top 50 Drupal 7 modules included in core. Backdrop also includes proper configuration management for quick and easy deployment of settings changes along with code.
Backdrop CMS has been out for more than 3 years, and has seen 9 on-time releases that have added more new core features - including a few you won't find in Drupal 8 (yet). Backdrop core includes built-in automatic URLs, page redirects, and a tool for adding new modules directly from your existing site. Backdrop also includes an updated administrative theme, a new front-end theme, dozens of User Experience improvements, and improved APIs for developers. Plus, Backdrop has a dragon!
Backdrop is an affordable alternative for upgrading existing Drupal sites. Backdrop will always provide an upgrade path (via update.php) and maintains 80% code compatibility between major versions. Decreasing the amount of time spent on development, maintenance, and upgrades will help keep costs down. Backdrop CMS is committed to making sure the small to medium sized businesses and non-profits have a full-featured and powerful CMS too.