The Working Group is using GitHub for its drafts and issue discussion: https://github.com/w3c/webauthn. The current Editors’ Draft combines the deliverables into a single draft spec, available at http://w3c.github.io/webauthn/.
We meet weekly on Wednesdays (1700 UTC, 1300 Boston) by phone and in the #webauthn channel on irc.w3.org. Calls and agendas are announced on the mailing list.
New participants are always welcome to join the group.