NuoDB is a SQL-oriented transactional database management system designed for distributed deployment in the cloud.
A relational database management system (RDBMS) is a collection of programs and capabilities that enable IT teams and others to create, update, administer and otherwise interact with a relational database.
A relational database is a set of formally described tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables.
VoltDB is an in-memory database. The software is available in an open-source community edition and in a commercial release from vendor VoltDB Inc.