FreeCAD -

 CADEMIA Community edition is an open source CAD software. CADEMIA was originally designed at the Bauhaus University in Weimar for teaching and research purposes. CADEMIA offers a professional developer framework as well as the necessary stability to be used in daily work and planning routines. It is simply 2D CAD software which provides many possibilities to extend via modules. It reads and wtites only into it's own file format. It is written in JAVA so it is independent on platform. CADEMIA is interesting JAVA application which is possible  to integrate into existing applications.