SpiderFoot - Open source intelligence (OSINT) automation tool.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
sn0int - sn0int is a semi-automatic OSINT framework and package manager
draw.io - Online diagramming application
Maltego - Maltego is an open source intelligence and forensics application.
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.