ObjectBox - ObjectBox empower edge computing with an edge device database and synchronization solution for Mobile & IoT. Store and sync data from edge to cloud.
HSQLDB - hsqldb: Full-featured 100% Java ORDBMS
Clustrix - Clustrix is the leading scale-out SQL database engineered for the cloud.
Axisbase - Axisbase is a database framework that you can use to track whatever sort of data your business manages.
Titan Database - Titan : Distributed Graph Database
FerretDB - FerretDB is an open-source proxy, which is an alternative to MongoDB.