It also contains hooks for local code in a cleanfeed.local file, so you can add your own filters and have them survive an upgrade of the main program. Cleanfeed is open-source. There are cool Hippo T-shirts. Note that, on INN, it is possible to run both Cleanfeed and Hippo on the same server. Running standalone on Highwind servers, you'll have to choose one or the other.
Some people run one filter on a transit server, and the other on a reader server.
Sources close to Highwind tell me there will be a filter multiplexer in the near future. I'm a spammer, and Cleanfeed is blocking my posts. If you don't understand what spam is, or believe that what you are doing is not spam, please contact your news administrator or upstream ISP for more information. They should be your first stop, since it is your contract with them that you are very probably breaking. You can also ask about the situation in the newsgroup news.admin.net-abuse.usenet .