Interactive (in your browser via WebAssembly) demo is here: https://www.endatabas.com/demo

Follow the tutorial at https://docs.endatabas.com/tutorial/sql_basics - so start with this:

    insert into posts (id, user_id, text) values (123, 456, 'Hello World');

(Which will create the table automatically)

Then:

    select * from posts;

It's AGPL licensed and written in Common Lisp, looks like it's been in development for just over a year: https://github.com/endatabas/endb

On disk storage format is Apache Arrow.