The Soundplane 8x8 is a force-sensing surface you can build yourself. It's made from wood, rubber, copper and plastic. It's entirely passive, meaning that there are no electronics inside that require power. Instead, an eight-in, eight-out audio interface along with DSP software is used for sensing and calibration.
Please see the NIME 2009 paper, written by Randy Jones and colleagues at the Univeristy of Victoria, for more information and construction tips. A more thorough, step-by-step guide is planned, but the information here should be enough to get your controller started. If you have questions, get in touch via our forums.
The software requires Max/MSP/Jitter to run. The Max/MSP/Jitter SDK is needed to compile it. All of this software is Mac only, but should be easy to port to Windows. I'm releasing it under the MIT License, which basically says: reprinting or use of the software must be attributed, and the software comes with no warranty.
There is a lot of tolerance in various parts of the design, including thickness of materials. If you can find something close to what is specified, try it!