EagleCAD is a CAD program written in C++ with Qt 4.8+ that runs on Linux, Mac, and Windows. The program incorporates a physics engine to help you find weaknessess in a structure before it is too late. It also renders via OpenGL which allows it to run on just about any system that can display graphics!
EagleCAD promises to also open/save 99% of 3D formats. Allowing you to easily transfer projects from any program to EagleCAD!