Dia is a good program to create diagrams. It has a number of standard charts: diagrams to build the network cards, process diagrams and UML. Dia is a good free alternative to Visio. The program supports a variety of formats.
The program is a part of GNOM but also available for Windows. The program supports creation of a large number of different diagrams (UML, ER, IDEF0), the full list is as follows
Objects for each chart are presented on panels. It is quite simple to drag and connect them.
To edit the properties of the chart elements commonly used standard dialog parameters such as: background, font, text, and others. For more complex elements used more dialogue, such dialogue to UML
All changes made in the dialog will be displayed directly on the chart.
Dia has a set of standard elements such as text, arrows, rectangular areas, ellipses, etc. It is not quite comfortable to use arrows, especially when dragging objects.
Dia is a pretty good alternative to Visio. Sometimes, the application is not convenient to work with, but you may get used to it very quickly.