NuoDB is one of the leaders in SQL-based transactional database systems. Since their founding, they have been pioneers in putting relational databases into distributed cloud systems. Their technology is cutting edge, yet still tempered with years of experience in the database industry.
NuoDB is a distributed database, accessible from anywhere, secure, and saved in the cloud. It also takes traditional SQL databases a step farther with a three tiered system that includes administrative, trasactional, and storage tiers. This helps NuoDB deal with some of the problems found in especially large cloud-based systems. It also uses a number of in-memory caches. This helps to maintain data integrity, while still operating within a cloud environment.
The cloud database from NuoDB comes in three flavors: an open source version that is free, a professional version for developers, and an enterprise edition for large corporate and manufacturing environments. Each one has the basic technology and makes use of the cloud-based design.