This is some piece of software I wrote about a year ago for a German massive forming technology company. Luckily, they agreed to make this software available under the GNU GPL. To my knowledge, it is the only GPL-licensed software for statistical process control.
Unfortunately I didn't have the time to write any decent documentation or put up a homepage for that software so far. I will to do so shortly.
During the last week, I was contracted to extend GSPC to support up to 16 inductive displacement transducers, and support multiple data acquisition boards per system.