SQLite (
https://www.sqlite.org/) is quite compact, mature, and public domain, it also gives you the option of in memory or on file space for storing the data base information. It is missing some feature of a full SQL implementation however, mySQL licensing seems a bit iffy (
https://en.wikipedia.org/wiki/MySQL) with Oracle running the show and postgress (
https://www.postgresql.org/) is enormous. SQLite also allows you to collect objects into a uniform file (IE the tables blobs etc.) which could be useful for distributing 'server' file sets I suppose. I'll go back to lurking. Mars