FreeCAD - An open-source parametric 3D modeler
PlanSwift - PlanSwift allows contractors to create accurate project estimates specific to their individual trade.
SketchUp - 3D for Everyone
Methvin - Project management and estimating tool designed for the construction industry.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Corecon - Corecon offers integrated estimating, project management, and job costing for small to medium-sized construction companies.