DraftSight is a simple 2D CAD program, and FreeCAD and OpenSCAD are full-fledged 3D CAD software suites. Free versions of SketchUp are also popular, particularly for home design and other tasks.
People looking for free and open source programs might want to consider FreeCAD, a full-fledged 3D CAD program appropriate for professional work. While FreeCAD is a viable option for home design and architectural tasks, it's especially popular for mechanical engineering tasks. OpenSCAD is another popular option. Support for scripting makes it a great option for power users, and it's popular for designing machine parts and other industrial tasks.
SketchUp Make is a powerful CAD programs that's free for students and people interesting in learning how CAD works. While it offers support for a range of CAD tasks, it's especially popular for people looking for stylized images. Easy exporting features help users make images for websites and presentations. Those looking to learn a CAD program can also download a version of SketchUp Pro for free.
Users looking for powerful 2D CAD programs can consider DraftSight. Although its lack of 3D features makes it inappropriate for industrial CAD or product design, it's viable for designing a room's layout. DraftSight also offers advanced exporting features, making it easy to use with other CAD programs.