The software (aka "tools" in the trade lingo) you will be using to recover the information is found among Computer Forensics enthusiasts.
There are PLENTY of Open Source solutions available. In fact, most of the best tools available in the Forensics field are FOSS.
The two that end up outperforming the closed source tools most in head-to-head match-ups are:
The Sleuth Kit and The Coroner's Toolkit
Here's just one quick place to go for all the necessary links as well as further general info: http://www.opensourceforensics.org/tools/unix.html
Oh... btw... Do NOT use the hard drive any more until you can use the forensic tools on it. Every time you start up the computer and do things on it you run the risk of writing over the top of the area's where the old files were. Once you've done that it becomes progressively harder to recover.