The RepRap is the first self-replicating manufacturing machine and with a bit of patience you too can build your own RepRap.
RepRap takes the form of a free 3D desktop printer capable of printing plastic objects. Since many parts of RepRap are made from plastic and RepRap prints those parts, RepRap self-replicates by making a kit of itself – a kit that anyone can assemble given time and materials. This means that if you’ve got a RepRap you can print one for a friend (RepRap Wiki 2012).
RepRap is a community project so you can get involved and get help as well as see plans and videos.
There’s also a link here to a visual guide from Gary Hodgson to the simplest and cheapest RepRap to build, the Prusa Mendel and a links to some RepRap books that help you learn more about the history and development of RepRap.