VoltDB

Created by DBMS R&D pioneer, Mike Stonebraker, VoltDB is a next-generation open-source DBMS that scales way beyond traditional databases, without sacrificing SQL or ACID for transactional data integrity. VoltDB is for database applications that support fast-growing transactional workloads and require:

Orders of magnitude better performance than conventional DBMS
Linear scalability
SQL as the DBMS interface
ACID transactions to ensure data consistency and integrity
High availability 24x7x365
With VoltDB you can develop and deploy applications at low cost and then scale them to handle millions of transactions per minute, and without the costs of rip and replace DBMS or hardware upgrades, extensive tuning, or application redesigns. Just add additional servers to the VoltDB cluster.