draw.io - Online diagramming application
JFLAP - JFLAP is software for experimenting with formal languages topics including nondeterministic finite...
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Rin'G - Download Rin'G - A non-intrusive tool for the study of graph algorithms
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.
Rocs - Rocs aims to be a Graph Theory IDE for helping professors to show the results of a graph algorithm...