Dia is roughly inspired by the commercial Windows program 'Visio', though more geared towards informal diagrams for casual use. It can be used to draw many different kinds of diagrams. 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.
Visio is drawing software package that helps you with all of your drawing and graphing needs, part of Microsoft Office suite.
Download for free
http://live.gnome.org/Dia
Download for free
http://live.gnome.org/Dia
