What type of NoSQL database is best suited to store hierarchical data?

Question

What type of NoSQL database is best suited to store hierarchical data?

Say for example I want to store posts of a forum with a tree structure:

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Answer 1

Graph databases would probably also solve this problem. If neo4j is not enough for you in terms of scaling, consider Titan, which is based on various storage back-ends including HBase and should scale very well. It is not as mature as neo4j, but it is a very promising project.