FeynArts (Popularity: )
http://www.feynarts.de/ Mathematica package for generation and visualization of Feynman diagrams and amplitudes.
FeynDiagram.com (Popularity: )
http://feyndiagram.com/ Free C++ library for drawing Feynman diagrams. The output is in PostScript, which can be used in TeX or printed ...
Povama (Popularity: )
http://povama.sourceforge.net Persint OpenGL Visualization for ATLAS Muon Analysis. Software used to visualize the reconstruction of muon traces.