yEd Graph Editor!

Lucidchart is an online diagram and flowchart software that supports Microsoft Office Visio import and can work on any operating system. The easiest way to draw flowcharts, wireframes, UML diagrams, network diagrams, mind maps, iPhone mockups, site maps and more. Work together in real time with your team and clients! Along with the online version, Lucidchart also has a downloadable solution that runs on Mac, Windows and Linux; this enables offline editing at any time! »

draw.io is a free online diagram drawing application for workflow, BPM, org charts, UML, ER, network diagrams. No login or registration are required and features include the ability to save locally (including svg), a range of stencils, .vsdx, Lucidchart and Gliffy import and real time diagram sharing.

Draw lets you produce anything from a quick sketch to a complex plan, and gives you the means to communicate with graphics and diagrams. With a maximum page size of 300cm by 300cm, Draw is a an excellent package for producing technical drawings, general posters, and much else.

Microsoft Office Visio makes it easy for IT and business professionals to visualize, explore, and communicate complex information. Go from complicated text and tables that are hard to understand to Visio diagrams that communicate information at a glance. Instead of static pictures, create data-connected Visio diagrams that display data, are easy to refresh, and dramatically increase your productivity.

Lucidchart is an online diagram and flowchart software that supports Microsoft Office Visio import and can work on any operating system. The easiest way to draw flowcharts, wireframes, UML diagrams, network diagrams, mind maps, iPhone mockups, site maps and more. Work together in real time with your team and clients! Along with the online version, Lucidchart also has a downloadable solution that runs on Mac, Windows and Linux; this enables offline editing at any time! »

Freeplane is a powerful and free software for building mind maps. It is a redesigned version of the well known FreeMind , and is created by one of FreeMind's key developers. The software is written in Java, and supports any platform capable of running current versions of Java.

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.

MindMeister is the market-leader in online mind mapping. Unlike traditional mind mapping tools, MindMeister allows for real-time brainstorming sessions between an unlimited number of users and requires only a standard web browser.MindMeister's intuitive editor is perfect for taking notes, brainstorming ideas, planning projects and outlining all sorts of texts. Users can choose between the classical mind map layout and org chart mode, and can export their mind maps into various formats like MS Word, PowerPoint, PDF, PNG etc. With its built-in presentation mode, users can also turn their mind maps into slideshows within seconds, and present them on the big screen or broadcast them to their collaborators. »

TheBrain helps you organize all your Web pages, contacts, documents, emails and files in a context-driven visual map.

Graphviz is open source graph visualization software. It has several main graph layout programs. It also has web and interactive graphical interfaces, and auxiliary tools, libraries, and language bindings.

Google Drawings, part of Google Drive , allows users to collaborate creating, sharing, and editing images or drawings. It can be used for creating charts, diagrams, designs, flow-charts, etc. It contains a subset of the features in Google Drive - Slides but with different templates. Its features include laying out drawings precisely with alignment guides, snap to grid, auto distribution, and inserting drawings into other Google documents, spreadsheets, or presentations. »

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.

Mindomo is the easiest online software for creating mind maps, concept maps, outlines and various other types of diagrams. The following features make it the perfect choice both for business and education:* real-time collaboration* you can work on maps even if your internet connection is down, and your changes will be automatically synchronized when the connection is restored* playback mode that shows you how a map was built* maps can be turned into presentations or real-time editable outlines* Google Apps and various LTI integrations (Canvas, Moodle, Blackboard, Desire2Learn, itslearning)* great variety of exports (PDF, RTF, PPT, TXT, OPML, MPX, HTML, ZIP, PNG, XLS, MOM, MM, MMAP)* Google Drive, Dropbox, FTP and ZIP backups »

The Visual Understanding Environment or VUE is a free, open source concept mapping application written in Java.