Although there are two products here (well, three, if you count the graphical interface and command line versions of the software) they’re provided as a bundle because of their related purposes.
TestDisk and PhotoRec
TestDisk is concerned with recovering partitions that have been lost from a disk, while PhotoRec allows for the recovery of photos and other files that have been lost due to deletion, formatting, or some other issue.
If your PC has been been struck by a virus that has rendered your hard drive inaccessible, these tools can – perhaps with the help of a second computer – help you to get things back up and running again. In case you need to call in the experts if TestDisk is not up to the task of recovery, it can still be helpful in terms of diagnostics.
File system support is impressive (FAT, NTFS, exFAT, ext2/ext3/ext4 and HFS+), and there are versions of the tools available for just about every desktop operating system you care to mention. File format support and recognition is also impressive, meaning that no matter what type of documents you're trying to get back from your mangled hard drive, you stand a very reasonable chance of success.
Free file recovery of this caliber is really hard to come by and therefore comes highly recommended.
It would be easy to criticise PhotoRec and TestDisk's command line interfaces, but considering what the tools are designed for, it can be excused. If you're happy to fiddle around trying to recover a boot sector or partition tables, you probably don't need your hand held too much.
That said, even in text-only mode, everything is reasonably self-explanatory. As this is recovery software, it should come as little surprise that there's no installation. These are essentially portable apps that you can run from a USB drive to avoid the risk of overwriting recoverable data. In tests, both programs proved to be not only pleasingly quick, but also highly reliable.
The latest version of TestDisk features several minor bug fixes and improved exFAT support. For full details, see the software change log.