It would be something of an understatement to say that open source software has been successful. This has led to many interesting attempts to translate that success into different fields, notably content (with things like Wikipedia) and data (the whole open data movement currently spreading through enlightened governments around the world.)
But one area that is proving slightly recalcitrant is that of open hardware. That's hardly surprising, since it involves analogue objects, which are scarce and relatively hard to share compared to purely digital ones.
Perhaps the most successful open hardware projects so far is Arduino:
Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.
According to Arduino:
Open-source hardware shares much of the principles and approach of free and open-source software. In particular, we believe that people should be able to study our hardware to understand how it works, make changes to it, and share those changes. To facilitate this, we release all of the original design files (Eagle CAD) for the Arduino hardware. These files are licensed under a Creative Commons Attribution Share-Alike license, which allows for both personal and commercial derivative works, as long as they credit Arduino and release their designs under the same license.
The Arduino software is also open-source. The source code for the Java environment is released under the GPL and the C/C++ microcontroller libraries are under the LGPL.
Note, though, that this is using off-the-shelf components to create Arduino boards; there is a level of open source hardware below this, which seeks to open up the components themselves. One long-running project aiming to do that for chips is OpenCores:
OpenCores is the world's largest site/community for development of hardware IP cores as open source.
OpenCores.org host the source code for different digital HW projects (IP-cores, SoC, boards, etc) and support the users with different tools, platforms, forums and other useful information.
Its latest project is ambitious:
The plan is to develop a complete SoC design (System-on-Chip) and implement it into an ASIC-component, and then offer it back to the OpenCores community as a "super-low-cost" processor based SoC ASIC-component, that can be used to develop commercial products without any restrictions or royalties. A development board will also be developed using this OpenRISC-ASIC running Linux, enabling users to develop complete cost-efficient Linux based products.
I don't really know enough about the details of chip design to comment on the feasibility of the project, or what its impact is likely to be: if you want to find out more, there's a FAQ, and detailed specifications [.pdf]. But it's certainly a good sign that the open hardware world is starting to contemplate projects like this. If you're interested, donations can be made on the project's main page.