1. MariaDB. https://www.mariadb.org/. MariaDB. https://www.mariadb.org/.
2. MySQL. https://www.mysql.com/. MySQL. https://www.mysql.com/.
3. PostgreSQL. https://www.postgresql.org/. PostgreSQL. https://www.postgresql.org/.
4. SQLite. https://www.sqlite.org/index.html. SQLite. https://www.sqlite.org/index.html.