SketchUp is a 3D modeling computer program for a wide range of drawing applications such as architectural, interior design, landscape architecture, civil and mechanical engineering, film and video game design. It is available as a web-based application, SketchUp Free, a freeware version, SketchUp Make, and a paid version with additional functionality, SketchUp Pro.
As is generally regarded, SketchUp is known for its beginner-friendly learning curve and features tons of tools for geometric objects. SketchUp also recently facilitated prepping and sharing 3D printable objects. There is, also, an online library of free model assemblies (e.g. windows, doors, automobiles), 3D Warehouse, to which users may contribute models.