Datomic - The fully transactional, cloud-ready, distributed database
MarkLogic Server - MarkLogic Server is a multi-model database that has both NoSQL and trusted enterprise data management capabilities.
Datahike - A durable datalog database adaptable for distribution.
Google Cloud Datastore - Cloud Datastore is a NoSQL database for your web and mobile applications.
Matisse - Matisse is a post-relational SQL database.
MySQL - The world's most popular open source database