Graphviz!

yEd is a powerful diagram editor that can be used to quickly create diagrams manually or import external data for analysis and auto-magically arrange even large data sets by just pressing a button. You can use yEd to quickly create flow charts, BPMN and UML diagrams, organization charts, mind maps, and many other kinds of diagrams, graphs, and networks. Choose from a wide range of highly sophisticated layout algorithms to automatically arrange diagrams in no time. An intuitive and visually appealing user interface makes creating diagrams fun. Once a diagram has been created, it’s easy to save, print, or export it to popular formats like PDF, SWF, EMF, SVG, JPEG, GIF, PNG, or HTML image maps. »

PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams. The generator can be run anywhere within JVM and integrated with various application such as wiki, text editor, IDE, programming language, documentation generator, and others. Mostly based on Graphviz. Can render various diagram syntax such as PlantUML, Dot, and Ditaa.

OmniGraffle can help you make eye-popping graphic documents—quickly—by providing powerful styling tools, keeping lines connected to shapes even when they’re moved, and magically organizing diagrams with just one click. Create flow charts, diagrams, UI and UX interactions, and more. Whether you need a quick sketch or an epic technical figure, OmniGraffle and OmniGraffle Pro keep it gorgeously understandable.

Gephi is an open-source software for visualizing and analyzing large networks graphs. Gephi uses a 3D render engine to display graphs in real-time and speed up the exploration. Use Gephi to explore, analyse, spatialise, filter, cluterize, manipulate and export all types of graphs.

UMLet is an open-source UML tool with a simple user interface: draw UML diagrams fast, export diagrams to eps, pdf, jpg, svg, and clipboard, share diagrams using Eclipse, and create new, custom UML elements.

A graph visualization library using web workers and jQuery

Diagrammix is a tool for efficiently building attractive diagrams.

Tulip is an information visualization framework dedicated to the analysis and visualization of relational data. Tulip aims to provide the developer with a complete library, supporting the design of interactive information visualization applications for relational data that can be tailored to the problems he or she is addressing. Written in C++ the framework enables the development of algorithms, visual encodings, interaction techniques, data models, and domain-specific visualizations. One of the goal of Tulip is to facilitates the reuse of components and allows the developers to focus on programming their application. This development pipeline makes the framework efficient for research prototyping as well as the development of end-user applications. »

Delineato - the italian word for "outline". Designed using the WYSIWYN paradigm - What You See Is What You Need - this carefully crafted application is targeted at creating simple diagrams, mind maps, brainstorming, to-do lists, architectural diagrams.A clutter-free interface allows you to concentrate and focus on the essence of your work.

KeyLines is a JavaScript toolkit used by developers to build powerful network visualization applications, quickly.

blockdiag and its family generate diagram images from simply text file.

Lets you easily draw a diagram - mind map, concept map, or flow chart - and convert it to a text outline, and vice versa.

As the easiest way to explore graph data, Linkurious technology helps you make sense of your data through a simple web-based interface. Companies can quickly visualize their data with Linkurious Enterprise or build their own application with the Linkurious SDK:

Neoclipse is a standalone workbench application to interact with Neo4j (database directory or server). It supports Cypher, index searches, visualisation, graph updates.

Data and relationships are everywhere, among members of an organization, devices in a network, components and systems in an aircraft or an automobile, and vendors in a supply chain. Customers with needs in link analysis, network topology, schematics and models, and dependencies, flows, and processes rely on our pioneering graph visualization and analysis expertise, and our data visualization capabilities. We help you gain new understanding from your data and enhance your applications. We offer mature and proven products, comprehensive services, and excellent technical support to help you succeed. »