TestDisk 
TestDisk is a free software for recovering data and is licensed under the terms of GNU General Public License (GPL). Initially, it was designed to recover data lost in storage partitions and to make non-booting disks bootable again. This is done when the storage medium is affected by viruses or software issues. TestDisk can repair any errors in the Partition table; in simple words, this software can be used to recover lost partitions on hard drives. 
 
Why you must get it: 
The application has features that appeal to both, experts as well as novices. For people who know little or nothing about data recovery techniques, Test-  Disk can be used to collect detailed information regarding the non-booting drive. This information can be analyzed by technical support professionals for more clarity regarding the problem. People familiar with Techdesk also find it a handy tool for onsite recovery.