This area is still incomplete. More here to come.
Parametric 3D Modeling Software
Should you not have the money or the budget to do some parametric 3D modeling. It has a bit of a learning curve but what CAD package doesn’t? FreeCAD has some great functionality and once get over the initial hump and understand it a little, you can take off pretty quick.
3D Printer Control Software
Cura is a software solution for 3D printing. While it is developed to be used with the Ultimaker 3D printer, it can be used with other RepRap based designs. Cura helps in setting up an Ultimaker, shows 3D models, allows for scaling / positioning, can slice the model to G-Code, has editable configuration settings, and send this G-Code to the 3D printer for printing.
LeoCAD is a Cross Platform, Open Source, easy to use and intuitive CAD application with an interface that is designed to allow new users to start creating new Lego models without having to spend too much time learning the application. It has a rich feature set that enables experienced users to build models by using techniques that are more advanced. LeoCAD is fully compatible with the LDraw Standard and related tools, and it reads and writes LDR and MPD files so that you can share and download models from the Internet. It also uses the LDraw parts library, which has almost 10,000 different parts and continues to receive updates. Versions available for Windows, Linux and macOS to ensure that users are familiar with the program interface.
Since LeoCAD is open-source, contributions for fixes and features are welcome and it will always remain free.