TestDisk download contains TWO programs - TestDisk and PhotoRec. They are used on the command line in the Terminal. As a result, these programs are designed for support personnel and experienced Mac users.
The TestDisk program is powerful free data recovery software! It was primarily designed to help recover lost partitions and/or make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally deleting a Partition Table).
It will also find accidentally deleted partitions (either Apple Partitions, the newer EFI partitions and Windows MBR Partitons) and provide the necessary information for you to restore them using the Apple pdisk command (for Apple Partitions) or the gpt command for (for EFI partitions)
PhotoRec is file data recovery software designed to recover lost files including video, documents and archives from Hard Disks and CDRom and lost pictures (thus, its 'Photo Recovery' name) from digital camera memory. PhotoRec ignores the filesystem and goes after the underlying data, so it will still work even if your media's filesystem has been severely damaged or re-formatted.
PhotoRec can recover data from various filesystems including FAT, NTFS and HFS+.