Summary: NoSQL is a terrible term for a collection of widely varied databases. You have key-value stores like Redis, Tokyo Cabinet, Memcached, etc. You also have document databases like couchDB and mongoDB. Finally you have column based systems like Cassandra. And still others like HBase. In a lot of cases, there are gems for these. I've used several of them such as the gems for managing Cassandra, couchDB, and mongoDB.
