Graphviz Alternatives

PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.

Online diagramming application

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.

Gephi is an open-source software for visualizing and analyzing large networks graphs.

LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.

Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.

The JavaScript toolkit for graph visualization

UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.

OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.

UMLet - Free UML Tool for Fast UML Diagrams

StarUML

ArgoUML, free and safe download. ArgoUML latest version: Open-source diagramming application for personal computers. ArgoUML is a program that allows users to create complex and professional diagrams.

Gaphor is a Python-based, open source, multiplatform and multipurpose modeling application for creating nice UML diagrams for documentation.