This bot scanned for anyone leaving a comment on Reddit that just says "Wrex" and replied with "Shepard". This was not a very good bot, pretty annoying actually. He was retired very quickly.
This bot scanned for anyone linking to a game on steampowered.com and followed the link in order to scrape the page for specific details about it. It would then reply to the original poster's comment with a neatly formatted table containing important details about the game. The idea was that people wouldn't need to follow the links in order to learn about the game. In practice, about half of the feedback I got was positive, and half was extremely negative - citing the large amount of space taken up by the bot's comments as being disruptive.