Followup to irc discussion on that topic: there is already anonymous mode in forums, although I only got it to work by granting forum_create and forum_write on the forum to the Unregistered Visitor and reverting a recent change to forums-security-procs like this:
tils@rbfm:/var/lib/reboot.fm/rubi/packages/forums$ cvs diff tcl/forums-security-procs.tcl
cvs diff: warning: failed to open /home/tils/.cvspass for reading: No such file or directory
Index: tcl/forums-security-procs.tcl
===================================================================
RCS file: /cvsroot/openacs-4/packages/forums/tcl/forums-security-procs.tcl,v
retrieving revision 1.7.2.2
diff -r1.7.2.2 forums-security-procs.tcl
65c65,67
< return [permission::permission_p -party_id $user_id -object_id $forum_id -privilege create]
---
<blockquote> # quick fix for the custom priv mess: revert to check for
# forum_create instead create -til
return [permission::permission_p -party_id $user_id -object_id $forum_id -privilege forum_create]
</blockquote>
81c83,85
< return [permission::permission_p -party_id $user_id -object_id $message_id -privilege write]
---
<blockquote> # quick fix for the custom priv mess: revert to check for
# forum_write instead write -til
return [permission::permission_p -party_id $user_id -object_id $message_id -privilege forum_write]
</blockquote>