bioRxiv is in beta.  This is from their “about” page:

“bioRxiv (pronounced “bio-archive”) is a free online archive and distribution service for unpublished preprints in the life sciences. It is operated by Cold Spring Harbor Laboratory, a not-for-profit research and educational institution. By posting preprints on bioRxiv, authors are able to make their findings immediately available to the scientific community and receive feedback on draft manuscripts before they are submitted to journals.

Articles are not peer-reviewed, edited, or typeset before being posted online. However, all articles undergo a basic screening process for offensive and/or non-scientific content. No endorsement of an article’s methods, assumptions, conclusions, or scientific quality by Cold Spring Harbor Laboratory is implied by its appearance in bioRxiv. An article may be posted prior to, or concurrently with, submission to a journal but should not be posted if it has already been published.

Authors may submit a revised version of an article to bioRxiv at any time and can update the bioRxiv record with a link to a version of an article that has been published in a journal. Once posted on bioRxiv, articles are citable and therefore cannot be removed.”

From an email/ad from Cold Spring Harbor Laboratory Press