Things on this page are fragmentary and immature notes/thoughts of the author. Please read with your own judgement!
SQLite
Apache Derby
H2
HSQLDB
References
https://www.baeldung.com/java-in-memory-databases
https://www.quora.com/Would-you-use-Apache-Derby-or-SQLite-for-a-single-file-embedded-database-for-your-Java-application
https://www2.sqlite.org/cvstrac/wiki?p=SqliteVersusDerby
https://db-engines.com/en/system/Derby%3BH2%3BSQLite
https://dzone.com/articles/3-java-embedded-databases
https://www.baeldung.com/java-in-memory-databases
https://db-engines.com/en/system/Derby%3BSQLite