Initial implementation is up, still rough around edges but works:
https://github.com/discourse/discourse/commit/f5d89169e2680da16a47c6a75ee21a9a2aebf472
You must enable allow_anonymous_posting site setting AND set anonymous_posting_min_trust_level to an appropriate level.
We keep track of a shadow “anonymous” account but there is no way of telling who it is unless you cross correlate IP addresses in the admin interface. This anon account can still be banned and so on if it gets out-of-hand.
