Open source software for experimental physics

jmizrahi writes: "I've recently started working in experimental physics. There are quite a few programs used in the lab, for assorted purposes--Labview, Igor, Inventor, Eagle, just to name a few. I've noticed that they're all proprietary. This seems to be standard practice, which surprised me. Does anybody know of any open source software intended for scientific research? Does anybody work in a lab that makes an effort to use open source software?"