DIA is a cross-platform open-source diagramming tool.
DIA is an open-source diagramming tool, inspired by Visio.
It currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and many other diagrams. It is also possible to add support for new shapes by writing simple XML files, using a subset of SVG to draw the shape.
Dia available for Windows, Mac OS X and Linux from: http://dia-installer.de