Wikipedia
VoCore
The VoCore is "a coin-sized Linux computer with wifi". It is a single-board computer developed in China. It includes WiFi (2.4 GHz 802.11 b/g/n), Ethernet (10/100 Mb/s x2), USB 2.0 (up to 480M) and 28 GPIO (reused).
It is entirely open source. Both the hardware and the software are available on the VoCore website.