3D parametric modeler
FreeCAD is a 3D parametric modeling application. It is primarily made for mechanical design, but also serves all other uses where you need to model 3D objects with precision and control over modeling history.
FreeCAD has been under development since 2002, and it offers a large list of features. Capabilities are still missing but it is powerful enough for hobbyist use, and small workshops. There is a fast-growing community of enthusiastic users who participate in the FreeCAD forum, and you can find many examples of quality projects developed with FreeCAD there. See also, FreeCAD used in production.
Like all free software projects, FreeCAD depends on its community to grow, gain features, and fix bugs. Don't forget this when using FreeCAD; if you like it, you can donate and help FreeCAD in various ways, such as writing documentation and making translations.