Oracle Database is an RDBMS. An RDBMS that implements object-oriented features such as user-defined types, inheritance, and polymorphism is called an object-relational database management system (ORDBMS). Oracle Database has extended the relational model to an object-relational model, making it possible to store complex business models in a relational database.

Riak is a distributed database designed to deliver maximum data availability by distributing data across multiple servers. As long as your client can reach one Riak server, it should be able to write data. In most failure scenarios, the data you want to read should be available, although it may not be the most up-to-date version of that data.

ClustrixDB is a scale-out SQL database built from the ground up with a distributed shared nothing architecture, automatic data redistribution (so you never need to shard), with built in fault tolerance, all accessible by a simple SQL interface and support for business critical MySQL features – replication, triggers, stored routines, etc.