Compares Apache Hbase and Apache Cassandra. Also compares MongoDB with Couchbase. I know essentially nothing about any of these and I think it makes a good point. (I do have a certificate in GIS, which is database stuff, and also worked had a job that involved accessing multiple databases, so not entirely alien. But I don't code these things.)
Edit: Oh, and, not surprisingly, they are singing the praises of their product. I don't have an issue with that. I kind of expected it. But, hey, believe in your product or do something else, you know?