Many years ago I tweeted something about a project I was working on, tagging #HTML5 and #CSS3 or something like that. There as a Twitter bot that retweeted anything with an #HTML5 tag, and another, seemingly independent bot that retweeted anything with #CSS3. They didn't keep a list of seen tweets. I really enjoyed watching them retweet each other for a few hours until someone intervened. (Thankfully the bots were both on batch jobs that ran every 10 minutes or so and not streaming off the firehose or some similar, more focused streaming endpoint.)