VTK, the Visualization Toolkit, is an open source software that provides a powerful framework for the computer graphic, for the images processing and for 3D rendering. It is widely used in the world and so it has a very large community of users; besides the Kitware (The Kitware homepage can be found here: https://public.kitware.com) company provides professional support. The toolkit is written in C++ and a lot of porting/wrappers for Tcl/Tk, Java and Python are provided; unlucky there aren't wrappers for Fortran, Fotran programmers must rely on mixed languages approach.

Because of its good features the VTK toolkit has been used to develop a large set of open source programs. An important family of programs is the scientific visualization programs. A lot of high-quality scientific visualization tool are available on the web and among them one of the best is ParaView, that it is one of the best scientific visualization program in the world and it is open source! Paraview is based on VTK.

ParaView is an open source software voted to scientific visualization and able to use the power of parallel architectures. It has an architecture client-server in order to make easy the remote visualization of very large set of data. Because it is based on VTK it inherits all VTK features. ParaView is very useful for Computational Fluid Dynamics visualizations because it provides powerful post-processing tools; it provides a very large set of importers for the most used format like Plot3D and HDF (the list is very large). It is easy to extend ParaView because it supports all the scripting language supported by VTK.