Contraptor is a DIY open source construction set for experimental personal fabrication, desktop manufacturing, prototyping and bootstrapping.

Various сartesian robots can be assembled from Contraptor and used as a prototyping platform for projects such as XY plotter, mini CNC machine, 3D printer, etc.

From the archive:

Fab@Home is a website dedicated to making and using fabbers - machines that can make almost anything, right on your desktop.

Neil Gershenfeld:

Students are desperate for hands-on experience.

Recently:

The 'Bus Pirate' is a universal bus interface that talks to most chips from a PC serial terminal, eliminating a ton of early prototyping effort when working with new or unknown chips.

From earlier this year:

The Arduino open-source microcontroller platform can be programmed and equipped to perform a nearly endless list of functions.

From 2004:

This class teaches the use of several types of CAD/CAM machines, and techniques for making literally 'almost anything'. The lecture notes include valuable tips on how to make those machines work, and links to other web sites with detailed information on the world of CAD/CAM.

Contraptor