SQLite

Reference - https://www.sqlite.org/index.html

What is SQLite?

SQLite is a database engine. 
It is software that allows users to interact with a relational database. 
In SQLite, a database is stored in a single file — a trait that distinguishes it from other database engines. 
This fact allows for a great deal of accessibility: copying a database is no more complicated than copying the file that stores the data, sharing a database can mean sending an email attachment.

Uses for SQLite

SQLite is used worldwide for testing, development, and in any other scenario where it makes sense for the database to be on the same disk as the application code.