Jonathan Ellis reviews in the NoSQL Ecosystem the origin of the NoSQL movement and 10 different NoSQL products and how their 1) support for multiple datacenters, 2) the ability to add new machines to a live cluster transparently to the your applications, 3) Data Model, 4) Query API, 5) Persistence Design. The 10 systems reviewed are: Cassandra, CouchDB, HBase, MongoDB, Neo4J, Redis, Riak, Scalaris, Tokyo Cabinet, Voldemort.
A very thorough and thoughtful article on the entire NoSQL space. It's clear from the article that NoSQL is not monolithic, there is a very wide variety of approaches to not being a relational database.
- NOSQL = Not Only SQL?. Google Groups thread on talking about the appropriateness of NoSQL as a label.
- The "NoSQL" Discussion has Nothing to Do With SQL by Michael Stonebraker.
- HBase vs. Cassandra: NoSQL Battle! by Bradford.
- Predictions on the future of NoSQL by Aleksander Kmetec.