Amazon Aurora is a relational database offered as a service integrated in AWS's Relational Database Service. Based on the open source MySQL, it is a commercial database that claims to be compatible with MySQL and PostgreSQL while providing superior throughput. As a cloud service, Aurora promises high availability. The system is being actively maintained and updated by Amazon.
Aurora was announced on Nov. 12, 2014 in Amazon's re:Invent conference in Las Vegas. It's officially released and ready to use as a service in AWS on July 27, 2015 by being added into Amazon Relational Database Service. A major patch of Aurora was added in October 24, 2017, where Aurora was extended with PostgreSQL compatibilities.
Aurora is stated to be a relational database engine. That can also be inferred from its full inheritance of MySQL/InnoDB's database engine and storage layout.
Aurora decouples the storage engine from its database engine, and the concurrency control protocol is entirely decided by the database engine it used. In the paper that introduced Aurora, the concurrency control model was stated to be exactly the same as the database engine it inherited from. So Aurora has the same concurrency control protocol, MVCC, as MySQL/InnoDB does.