Gephi - Gephi is an open-source software for visualizing and analyzing large networks graphs.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
yEd Graph Editor - 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.
Visallo - Visallo helps intelligence analysts, law enforcement detectives, and fraud investigators produce...
draw.io - Online diagramming application