2
you are totally right. no forum module is released officially for xoops 256.
you have 2 unofficial choice:
1- newbb 4.3 Alfred stable version
http://www.simple-xoops.de/projekt/2:1-Forum_-_newBB.html
(there is a newbb 4.4 alpha version too for test)
2- newbb 4.33 irmtfan RC7 version:
http://svn.code.sf.net/p/xoops/svn/XoopsModules/newbb/branches/irmtfan/newbb/
you should choose yourself.
Edit:
personally, I will be glad if you could test my version of newbb and report back any issue or request.
It is mainly a debugged version of all older newbb versions include newbb 1, newbb 2, newbb 3.08, newbb 4, and newbb 4.3