Interesting new participant in the NoSQL space, OrientDB. What is OrientDB?
OrientDB is a new Open Source NoSQL DBMS born with the best features of all the others. It's written in Java and it's amazing fast: can store up to 200,000 records in 5 seconds on common hardware. Even if it's Document based database the relationships are managed as in Graph Databases with direct connections among records. You can traverse entire or part of trees and graphs of records in few milliseconds. Supports schema-less, schema-full and schema-mixed modes. Has a strong security profiling system based on user and roles and support the SQL between the query languages. Thanks to the SQL layer it's straightforward to use it for people skilled in Relational world.
In addition to the features above it supports transaction. A feature that is often missing from other NoSQL data stores. I’ve added links both to the code hosting site and the project site as well. One other piece of info is that OrientDB is the creation of one individual, which is both impressive and scary at the same time. While it is released with the Apache license and code is available it does not yet have a huge community supporting it.
Orient Home Page
Orient Project Page (Google Code)