As inspired by the bots on Reddit that respond to certain words, I've thrown together this code which allows anyone to set up their own response bot.
There is a bit more detail on Github, but in summary you can set your own trigger word and responses, and you have two modes of operation, "Exclude" which is the default and covers every community you're federated with (and allows moderators of a community to PM the bot to exclude it) and "Include", where you can pick a single community for the bot to be active in.
This is really early days and rough, but should work at the most basic level. Anyone who can provide some ideas/feedback/improvements - I'm totally open to them.
And to prove it works, I'm running Legolas Bot. Any comment you make below with the word "legolas" in will get a response (probably).
Small updates to reduce spaminess - will only reply to top level comments now.
Edit: Little updates include customisable polling rates and the ability to tag the comment creators name in a response.
And to prove it works: legolas
This Is No Mere Ranger. He Is Aragorn, Son Of Arathorn. You Owe Him Your Allegiance.