MySQL - The world's most popular open source database
Open DBDiff - A database comparison tool for Microsoft SQL Server 2005+ that reports schema differences and...
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
Replicator - Easily replicate database table data - even with heterogeneous databases.
SQLite - SQLite Home Page
TiCodeX SQL Schema Compare - SQL Schema Compare supports Database schema compare for MS-SQL, mySQL and Postgres and runs on Windows, Linux and MacOS