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Vtk [http://www.kitware.com/] is a powerful engine for scientific visualization.  It's open source.

It has used Tcl/Tk as an integration platform from nearly the beginning  [http://www.usenix.org/publications/library/proceedings/tcl96/martin.html].  It's also tightly integrated with Java and C++.

Its test suite, Dart, automates nightly regression [testing] and puts status displays on the Web [http://public.kitware.com/VTK/Testing/Dashboard/MostRecentResults-Nightly/Dashboard.html].  It, too, is open source and is discussed further on the [testing] page of the Wiki.