The "free software" that he used for the FPGA design itself is actually proprietary Xilinx software that they offer a free version with limited capailities, or in other words it's "free as in beer", meaning it doesn't cost anything as opposed to being open source software.

Are there "free as in speech" tools for FPGA development?

We did an article a while back on Icarus, a Free (as in speech) Verilog simulation and synthesis tool. You can do the design in Icarus and there are also GPL'd tools for downloading your code to chips like the Xilinx via JTAG. But, if memory serves, their is still one step along the way where you have to use a proprietary Xilinx tool to place-and-route and generate the configuration bit stream for the chip (it is, however, a free [as in beer] tool and can run on Linux under Wine). Hopefully, Xilinx will free the source to this tool or it will likely be reverse-engineered and freed anyway.

There is a Xilinx on Linux How-To that might have more details.

And you can probably find other Free (as in speech) CPLD and FPGA software at the OpenCollector.org site.

Andrey does not have a robots.net account, and asked me to post this reply to my comment:

In the article there is no confusion between "free as in ..." - I called Xilinx tools "free for download", not "free software". One of the goals of the article was to use an opportunity to influence Xilinx team in what I believe is right direction - towards use of really free software. I was pursuing the same in private emails and conversations also. I'm sure that better cooperation with free software development community (such as Icarus Verilog) can benefit Xilinx as (I think) 99% of their revenues come from hardware, not software sales. The only "limited capabilities" I encountered with Xilinx WebPACK was the simulator - it has 500 lines limit (camera sources have about 8000 of them) - and this is exactly the place where Icarus could fit. Unfortunately with later devices (Spartan 2e 400K and 600K) as most of the Spartan 3 series it is not true - they are not supported by even Xilinx native software.
Maybe we could join efforts to persuade Xilinx to turn more to the FS? In addition to the source of free (for Xilinx :-)) tools they might later bundle with their own, software developers curious to play with FPGAs might find new applications for Xilinx silicone.

Thanks for posting the update. I hope we can convince Xilinx to start using Free Software. A Xilinx rep gave a presentation at a recent DPRG meeting I attended and seemed quite positive about Linux in general.