#1 – Time Machine
You may think it's inappropriate to put Time Machine in the line of data recovery software on Mac. But I insist doing this and put it in the top first place. As you know, Mac computers manufactured after November 2007 are equipped with an important feature - Time Machine. The backup and recovery utility is able to backup almost everything on your Mac every hour with its unique functions. You can easily recover data from Time Machine backup once you deleted or lost your some critical files such as applications, documents, photos etc. Learn how to set up and restore backup from this Apple Support page. Most of the case Mac users tend to forget backup or not so interested in using Time Machine. So when you lost files by means of emptying Trash bin, quick formatted the drive, partition became inaccessible etc. without backup. The only way is to try a third-party mac data recovery software. Here are several file recovery freeware based on Mac.
#2 – MacKeeper Files Recovery
#3 – TestDisk & PhotoRec
TestDisk was primarily designed to help recover lost partitions and make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally erasing your Partition Table). PhotoRec is designed to recover lost lost files from external device (memory card, pen drive, removable disk), even hard disk and CDRom. As a result, if you have lost partition or strange problem with your hard disk partitions, try TestDisk. To recover lost digital pictures or files, try PhotoRec.Note: This recovery tool operates through command line (similar to DOS) without GUI. But it won’t be hard for you handle it as there are corresponding instruction texts within steps.Download TestDisk & PhotoRec from CNET.See TestDisk Step by Step Tutorial and PhotoRec Step by Step Tutorial.
#4 – Exif Untrasher
Exif Untrasher(version 1.4.3) is able to recover deleted or formatted photos(with only JPG format) from external device such as digital camera or USB flash drive etc on Mac OS X for free. But it won’t support internal Mac hard drive. So I’d like to tag it with “Digital Media JPG Photo Recovery for Mac”. This Mac recovery freeware can be used when you want to recover those lost JPEG photos from digital camera or camcorder etc if you have your own Mac machine. If your camera saves in the RAW format, you are out of luck.Note: versions 1.4 and newer will require Mac OS X 10.3 or newer. Language options: English, German, French and Italian.Download from its official site.
The programs talked above are completely freeware without any limitations though each has its own shortcoming. There are many other providers on the market claiming its products as "free Mac data recovery software" or "free version" but it's not real freeware.
[updated on 2012.1.30] "Also if you are comfortable with using paid Mac data recovery program, one of my Mac readers ever successfully recovered a lot of documents from a formatted Mac hard drive with the Mac data recovery software, programs with GUI(Graphic User Interface).You can take that a try if you are not used to handle through command line."
Not like Windows, few software manufacturers offer data recovery freeware on Mac OS X. But I hope it won't be too long for more freeware to float up as I believe "all software will be free one day". Once such truly free Macintosh data recovery software, I'll get you updated here.