ParaView is an open-source, multi-platform data analysis and visualization application. ParaView users can quickly build visualizations to analyze their data using qualitative and quantitative techniques.
Our favourite Post-processor is by far ParaView, the easy-to-use, good looking, efficient and flexible software initially developed by Kitware Inc. and Los Alamos National Laboratory. ParaView uses the Visualisation Toolkit (VTK) as its data processing and rendering engine and can therefore read any data in VTK format.
Some FEA codes use it as their main post-processing tool. For example, Salome (the Pre- and Post-Processing platform associates to code_aster) has a module called PARAVIS that integrates Paraview. The main post-processing tool provided with OpenFOAM is called paraFoam. It is strictly a script that launches ParaView using the reader module supplied with OpenFOAM.