SchemaCrawler is a free database schema discovery and comprehension tool. SchemaCrawler has a good mix useful features for data governance. You can search for database schema objects using regular expressions, and output the schema and data in a readable text format. The output serves for database documentation, and is designed to be diff-ed against other database schemas. SchemaCrawler also generates schema diagrams. You can execute scripts in any standard scripting language against your database. You can find potential schema design issues with lint.
SchemaCrawler supports almost any database that has a JDBC driver, but for convenience is bundled with drivers for some commonly used RDBMS systems. SchemaCrawler works with any operating system that supports Java 7 or better.
Consider supporting SchemaCrawler by making a donation.