Review on H2 Database Engine by Justin Sherman

It's easy to use, it has very good performance in terms of speed for queries that I need, and its free! The only downside about this product would be if you have multiple users sharing one machine (e.g., web server) or even more than 1 user using same computer at once.

If your app needs lots of concurrent connections with DBs like MySQL/Postgresql then go ahead and give hsqldb another try since they support connection pooling which will help tremendously when compared against other products out there such as DBeaver etc. We are solving an issue where we needed a tool to work well with our JDBC driver without having issues from time-to-time regarding connectivity errors or slow responses while doing data analysis jobs via HiveQL.