UML, network diagram, flowchart: http://projects.gnome.org/dia/ http://projects.gnome.org/dia/ Sequence diagram: http://sdedit.sourceforge.net/ http://sdedit.s

UML, network diagram, flowchart: http://projects.gnome.org/dia/ http://projects.gnome.org/dia/ Sequence diagram: http://sdedit.sourceforge.net/ http://sdedit.sourceforge.net/ Also for the corporate world where only Microsoft tools are an option, I tend to just use MS Word, you can make diagrams that are good enough to get the message across, yet everybody has access to it without requiring a special license.