PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
madge - Create graphs from your CommonJS or AMD module dependencies
mermaid - Generation of diagram and flowchart from text in a similar manner as markdown
dependo - Visualize your CommonJS or AMD module dependencies in a force directed graph report.
Gliffy.com is a web-based diagram editor. Create and share flowcharts, network diagrams, floor plans, user interface designs and other drawings online.
Simple web based ascii flow diagram drawing tool, draw boxes, lines, arrows and type, then export straight to text/html.
Diagramly is a free online diagram drawing application for workflow, BPM, org charts, UML, ER, network diagrams
BOUML : A free UML toolbox running under Unix/Linux/Solaris and Windows to specify and generate code in C++, Java, Php, Python and Idl