SSRN has launched the Biology Research Network (BioRN).
Here's an excerpt from the announcement:
Biology researchers are able to post preprints and working papers on BioRN, share ideas and other early stage research, and collaborate. It allows users to quickly upload and read abstracts and full-text papers, free of charge. A preprint is the author’s own write-up of research results and analysis that has not been peer-reviewed or had any value added to it by a publisher (such as formatting, copy-editing, technical enhancements). A preprint server, or working paper repository as they are also known, allows users to share these documents.