Windows 
Linux 
MacOSX 
Dia can be used to draw different type of diagrams. Dia contains shapes for UML and network diagrams and more but it can also be extended by adding new shapes.
Dia save diagrams in gzip XML files and can export in many format like PNG, SVG, EPS. It can also open diagram files from Visio and WordPerfect.
This tutorial is a good start point to understand how to use the power of Dia.
Dia screenshots
Bookmark this software:
