For a quick explanation, here is our original Kickstarter video, featuring an early prototype PressurePen rev1:
PressurePen is an open source hardware project funded, in part, by Kickstarter backers. You can see the Kickstarter page here. The campaign successfully raised its funding goal on May 31, 2012 with 105 individual backers and $10,264 raised of its $10,000 goal. My thanks go out to all of the backers, friends and family that helped get us to that goal.
The hardware and software for PressurePen are all open source. 3D files to print or modify your own PressurePen shell are available at Thingiverse. PCB design files and sample application code are available at GitHub. You can read more, including the license, on the source page.