MySQL - The world's most popular open source database
Supermetrics - Supermetrics condenses all the major vectors of data relevant to a user's marketing campaigns and helps them make sense of it all.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Airbyte - Replicate data in minutes with prebuilt & custom connectors
SQLite - SQLite Home Page
Fivetran - Fivetran offers companies a data connector for extracting data from many different cloud and database sources.