GSmartControl is a graphical user interface for smartctl (from smartmontools package), which is a tool for querying and controlling SMART.
License: Open Source
HDDScan is a Windows-only tool with a user-friendly interface and portability, making it easy to use for testing hard drives. In contrast, GSmartControl offers cross-platform compatibility and in-depth S.M.A.R.T. analysis, but may be more complex for novice users.