The DIYLILCNC is a fully functional, open source 3-axis CNC that you can build with basic tools and parts that can be locally sourced. The idea is that you develop a 3D design in a CAD application, put feedstock into the CNC, and print your design to it, and it cuts and grinds away everything but what your design is supposed to be. Total cost of construction is about $700us. You can download the plans and DXF template files from the website for free (they have a CC-BY-SA license).
Wikihouse is an archive of open source building designs contributed by engineers and architects around the world. Each design is peer-reviewed and analyzed by others to ensure that the designs are sound. Some of them have already been built and the results posted for further review. The design principles include being as easy to build by people with minimal formal training, as energy efficient as possible, and easy to modify to fit a particular purpose. All designs are made in Google Sketchup and can be cut with an automill if available.
This site collects CNC and laser cutter meshes that can be used to manufacture open source office and home furniture.
An open source DIY robotics/rapid prototyping kit much like an Erector set. Lots of standardized pre-milled bars, rods, connectors, and components. Build your own plotter, CNC machine, RepRap, scanner table, or what have you. Capable of three axes of linear motion. Comes with all the electronics you need, including an Arduino, stepper motors, and a motor driver board.
How to construct a CNC machine using foamcore board.
The Shapeoko is an open source CNC that you can either buy as a kit or build yourself for about $300us. Work up your design on a laptop using open source CAD software, clamp feedstock on the bed, and it'll produce what you designed. Because it's open source it's not limited to wood - it could be adapted to just about any material that you can cut or grind could be. Chances are, someone's already done it and posted the docs.
Everything is also kept in a respository on Github: https://github.com/shapeoko/shapeoko
lcamfuf wrote a book on some classic DIY/maker techniques for building stuff, such as CNC machining, mold making, and resin casting. Cost is a consideration in everything he wrote about so if you're not rich or well connected but want to get into building things, give this a read. You can read it chapter by chapter or all in one go.