I love chat bots. I wanted to learn more than just IRC. Discord is a very popular communication tool for gamers, it's pretty much Slack but with voice on top (I don't know the exact differences, but they are very similiar).
At the time, I was part of a community around a small YouTuber and I decided to build him a custom bot for his needs, while trying to learn as many new things as possible.
Working with the discord.py library was amazing, IRC running Twisted is completely different beast than this simple yet powerful API wrapper. The author made great use of many new things in Python 3.4+ and I knew that unless I needed 2.7 libraries, I always wanted to use Python 3 and learn more and more.
The bot is unfortunately not running anymore, but I learned a great deal and had a lot of fun writing it. I learned how to use Heroku a bit, wrote a simple unittest to see how Continuious Integration works out and more. I also learned what is it like to have somebody contribute to your code and trying to manage that. The biggest contributor was pretty unexperienced, so a lot of my time on the project was spent fixing/improving/cleaning up his code and helping him - which was also a very valuable lesson for me.