BleepingComputer Review:

TestDisk is a free hard disk partition repair and recovery tool.  This tool was created to recover lost partitions and fix partitions so that you can properly boot your computer again. TestDisk has since been enhanced to include many other features that include undeleting files, copying data from deleted partitions, and rebuilding the boot sector.

Product Description from CGSecurity:

TestDisk 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). Partition table recovery using TestDisk is really easy.

TestDisk can

• Fix partition table, recover deleted partition
• Recover FAT32 boot sector from its backup
• Rebuild FAT12/FAT16/FAT32 boot sector
• Fix FAT tables
• Rebuild NTFS boot sector
• Recover NTFS boot sector from its backup
• Fix MFT using MFT mirror
• Locate ext2/ext3/ext4 Backup SuperBlock
• Undelete files from FAT, exFAT, NTFS and ext2 filesystem
• Copy files from deleted FAT, exFAT, NTFS and ext2/ext3/ext4 partitions.

TestDisk has features for both novices and experts. For those who know little or nothing about data recovery techniques, TestDisk can be used to collect detailed information about a non-booting drive which can then be sent to a tech for further analysis. Those more familiar with such procedures should find TestDisk a handy tool in performing onsite recovery.