Open DBDiff - A database comparison tool for Microsoft SQL Server 2005+ that reports schema differences and...
MySQL - The world's most popular open source database
Redgate SQL Data Compare - Use Redgate SQL Data Compare to compare and synchronize static, lookup, and reference data in your SQL Server database - try it free
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
DataWeigher - The DataWeigher is the tool to compare and synchronize data.
SQLite - SQLite Home Page