SeaTools for DOS is a diagnostic tool that tests Seagate and Maxtor hard disk drives from DOS. It includes several tests to examine the physical media and detect any issues. The document provides instructions on booting from the SeaTools CD, selecting drives and tests to run, interpreting test results, and options for secure erasing or setting drive capacity. Key features include the short and long tests to check for defects, fixing bad sectors if found, and providing a SeaTools test code for warranty claims if a drive fails.