LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Terragen - Terragen is a scenery generator, created with the goal of generating photorealistic landscape...
FreeCAD - An open-source parametric 3D modeler
Vue - Create vast expanses of terrains, add trees, select the best point of view and render...
SketchUp - 3D for Everyone
DreamScape - Plugin for 3ds Max that creates skies, clouds, ocean waves, boat wakes, naval dynamics and terrain.