Programs like FreeCAD or LibreCAD for basic 2D work.
To download AutoCAD 2011 64-bit, you'll need to visit the Autodesk website or a trusted software repository.
If you never registered a 2011 license previously, this will not work. Autodesk does not give away old versions for free.
: Contacting the Autodesk Support team directly is the most reliable way for license holders to get a secure download link for legacy media [9, 12]. System Requirements for 64-bit Version
If you have a valid license, you should try these official channels first: Autodesk Account : Log in to the Autodesk Management Portal All Products and Services