QCAD is an opensource 2D CAD built with the framework application and objects library Qt by the first class developer Andrew Mustun. QCAD is available for Windows, Linux and MacOS platforms.
If you need to work with DXF and DWF files you can also purchase at a very reasonable price the QCAD Professional license which entitles you to use the 3d party libraries able to handle these commercial formats.
I suggest you to discover and learn more about this interesting product at the QCAD official web site.
If you need commercial info you can find everything at the RibbonSoft web site.
Don’t forget to visit the users forum here , where you can find a lot of answers and chat with the brilliant QCAD author.
It is possible to modify the user interface ( adding menus, dialog box,…) , it is possible to grab data from the drawings, it is possible to add drawing elements programmatically, your limit is only your fantasy and knowledge.
As contractor software developer I have acquired a certain grade of experience programming QCAD add-on and customization.