FreeCAD -

eCabinet Systems is a program established for professional custom cabinet makers and custom cabinet manufacturing companies.

eCabinet Systems uses rich, three-dimensional graphics in its design area. Detailed solid model cabinet images (samples) reflect every aspect of the design. As changes are made, you can move, rotate, zoom and explode the image to make sure design details are exactly what you want. Modified cabinets are saved, further modified and saved again, quickly creating entire libraries of custom designs. These cabinets are then accessed, resized and used in actual jobs.

K3DSurf is a program to visualize and manipulate Mathematical models in three, four, five and six dimensions.

K3DSurf supports Parametric equations and Isosurfaces.

Surface Evolver is an interactive program for the modelling of liquid surfaces shaped by various forces and constraints.
The program is available free of charge.

Liberta - timber construction software available for free
Roof framework creation in a few minutes!

...it looks really interesting - you have to try it.