SafeSQL is an SQL query processer to automate the tedious tasks of syntax testing, injection attack-proofing, dropping parts of queries and other misc features.
mysqldiff is a Perl script which compares the data structures (i.e. table definitions) of two MySQL databases and returns the differences as a sequence of MySQL commands suitable for piping into mysql which will transform the structure of the first database to be identical to that of the second.
KSqlAnalyzer is a tool for easy accessing the data of a MS-SQL-Database. The functionality and the look&feel are similar to the program 'SQL-Query-Analyzer' written by Microsoft.
Another PostgreSQL Diff Tool (also known as apgdiff) is free PostgreSQL diff tool that is useful for comparison/diffing of database schemas. The tool compares two database dump files and creates output with DDL statements that can be used to update old database schema to new one or to see in what both databases differ.
Goal of oraschemadoc is "JavaDoc" style detailed documentation for all objects in schema covering Oracle specific features. Result of execution of oraschemadoc is set of static html files. There are more features under development...
AQueryx is a cross-platform and cross-backend interactive query tool. The users of it are mostly database developers and administrators who need to quickly hand-code many SQL queries, modify database structure and query table data.