Several free tools are available to help with SQL tuning and performance diagnostics, including SQLd360, SQLT, and eDB360. SQLd360 and SQLT are good for diagnosing a single SQL statement, while eDB360 provides a 360-degree view of an entire Oracle database. Snapper and TUNAs360 can diagnose sessions and database activity. Standalone scripts like planx and sqlmon provide specialized diagnostics for individual cases. These free tools vary in size and capabilities, but all aim to help tune and diagnose SQL and database performance issues.