Botwiki is an impressive collection of bots for a variety of social networks and collaboration tools – Twitter, Slack, Tubmlr, Facebook and Messenger, YouTube, Reddit, Telegram, Snapchat, and more. You can browse all these by network or by category.
Here’s a random Twitter bot for you:
@holidaybot4000 is a Twitter bot that tweets holidays around the world for the given day, typically together with an image of the country’s flag.