dia lives in the dia locker, and is a very full featured diagram editor. It contains premade symbols for many of the contexts in which you might have to make one of these, including electronic circuits, civil engineering plans, flow charts, UML plans, and more. Click on ``chronogram'' to see the alternatives available. It has its own formats for saving work, but also saves in the Xfig format, (see above) and in a Tex related format. After you lay some elements on your dia canvas, you can move the points that define them in order to connect the elements together. The program will then let you move elements around while keeping hold of the topology you connected together.