If you only need basic Wiki functionality, there is an OpenACS module by Hafeez Bana - see
this thread.
Although it is for OpenACS 3.5.2, I was able to make it work with 4.5. It is PostgreSQL only. Other than splitting and moving files into 4.5ish locations, I removed the unneeded doc_return and ad_quotehtml definitions and changed all of the joins with the users table to joins with cc_users view. (It was looking for the first_names column.)
