I am one of the lead architects for Spider, a php-based graph database abstraction library similar to Eloquent or Doctrine. In getting ready for the first truly functional release, I thought I would share some great links to a crash course in Graph Databases as a whole. You can also check out by graphs tag for other posts about graph databases and php.
Some great resources:
The real purpose of this post was to repost this incredible breakdown of the top contenders for graph databases in 2015