On: Huly – Open-source project management platform

[KronisLV]

If you need a database that you can embed in Java, have a look at:

H2: https://www.h2database.com/html/main.html

HSQLDB: https://hsqldb.org/

Apache Derby: https://db.apache.org/derby/

Though those would certainly be a bit niche approaches, so you'll find that there are fewer examples of using either online.