Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
UCINET - UCINET for Windows is a software package for the analysis of social network data.
draw.io - Online diagramming application
Graphviz - Graphviz is open source graph visualization software. It has several main graph layout programs.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
NodeXL - Home