Open ExG

OpenHardwareExG: is a project that provides both open source hardware and software for the measurement and analysis of different types of biosignals

From the project page:

About the OpenHardwareExG project
Project goals
The main goal of the project is to build a device that allows the creation of electrophysiologic signal processing applications. In addition:

    Hardware and software that we develop will have a free/open source license. We also prefer to use hardware and software that are free/open source.
    We would like to keep the hardware "DIY compatible" (hand solderable, with parts that are readily available in small quantities, etc.)
    For us, this is a hobby and learning project. It's important to keep it fun, and take the time to learn along the way.

ExG board