OpenBSD
As of release 3.6, Arla is included in the default install of OpenBSD, but is only sufficient for client use. See This Article on http://www.undeadly.org for a brief bit of information on how to setup a client.
The unstable version of OpenAFS supports OpenBSD. Leading the porting effort is Jim Rees. Some relevant links:
* Rees' Website
* An old thread from the openafs-info mailing list dealing with compilation on OpenBSD 3.1
-- ClarkHale? - 16 Jan 2005