Source: http://backdropcms.org/Small-scale Drupal
Backdrop appeals to a different developer audience than Drupal 8. By rewinding APIs back a bit further (removing database query abstraction and page-level renderable arrays for example), Backdrop will lower its barrier to entry, increase performance, and position itself closer to the market of WordPress users.
Related links:
https://drupal.org/node/2117247
http://www.jenlampton.com/blog/introduc ... rupal-fork
2. Backdrop core code repository.Here's where you might disagree with me: Drupal 7 was too hard to learn. Drupal 8 will be harder just by its virtue of being more complex. I want there to be an easier alternative, for example: Backdrop CMS.
https://github.com/backdrop/backdrop
3. Documentation
http://handbook.backdropcms.org/
4. Backdrop CMS channel on YouTube
https://www.youtube.com/user/backdropcms
5. Backdrop on Twitter and G+
https://twitter.com/backdropcms
https://plus.google.com/107335894649589204558/posts