Nerves is still quite young and under very heavy development, but it is already powering rock-solid shipping industrial products. We are working diligently to have nerves ready for a wider audience by Q4 of 2015. In the meantime, if you are very hearty and interested in helping us craft nerves, contact us on the #nerves channel in the elixir-lang slack community or contact us on the mailing list.
Nerves is fully open source with a permissive (MIT) license. Nerves uses Buildroot to provide Linux, so some portions of the foundation are licensed under the GPL.