I recommend that you visit this course wiki. It contains free material relevant to participating in an open source projects. The course, "Open Source Software Practice" is a taught at RPI. http://public.kitware.com/OpenSourceSoftwarePractice

Complete nonsense: ParaView, ITK, CMake, CDash, Slicer, Titan, MIDAS, vxl, IGSTK, and more: all open source, some are toolkits, some are applications. These tools are in widespread use in production environments. The company teaches an open source course at RPI, and particpates in things like OSCON, etc.

Look into VTK and ParaView. Both open source packages (BSD license) from kitware (vtk.org and paraview.org). Historically they have been a scientific visualization system, but in the recent two years they have worked with Sandia Nat'l Labs to add an extensive information visualization subsystem. They major goal of the work is to make it scalable (using distributed parallel processing); something that's really important as data sets get large.