FreeCAD - An open-source parametric 3D modeler
e-Builder - e-Builder is a construction program management solution that manages capital program cost, schedule, and documents.
SketchUp - 3D for Everyone
RedTeam - RedTeam is a construction project management software specially designed for midsize commercial construction companies.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
PlanSwift - PlanSwift allows contractors to create accurate project estimates specific to their individual trade.