The ISCABBS RSS feeds are located at http://rss.iscabbs.com/
They are generated by a Ruby/Sinatra application named RaccFeeds, whose source code can be found at http://github.com/minter/raccfeeds/
The code consists of a backend script, run via cron, that polls both the database of stored posts and the live BBS, reconciling them (posts that have been removed from the BBS are marked as “deleted” in the database, new posts on the BBS are added to the database).
There is then a frontend process, written in the Sinatra web framework, to generate the actual RSS Feeds.