TestDisk and Photorec are powerful free data recovery software available for download under GPL license. TestDisk 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, etc).
While Photorec helps to recover lost files including video, documents and archives from Hard Disks and CDRom and lost pictures from digital camera memory, etc. Both the applications are available in a single package and run under Windows all, Linux, FreeBSD, Mac OSX and Sun Solaris.
Testdisk can perform the job like - 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 Backup SuperBlock.
Photorec recognizes numerous file format including ZIP, Office, PDF, HTML, JPEG and various graphics file formats and works with HardDisks, Cdrom, Compact Flash, Memory Stick, SecureDigital, SmartMedia, Microdrive, MMC, USB Memory Drives, etc.
Full documentation and other details available at Cgsecurity
However, in my opinion, this program is not very user friendly. We should have some knowledge about different file system, partition and all to operate it. However this is powerful software in this category and is free.
Requirement: Window all, Mac OSX, Linux, FreeBSD, Sun Solaris
License: Open Source
File size: 2.7Mb