I'd think lots of people would know LockoutBot. However, for those who don't, it allows you to form a custom contest and compete with your friends on Discord. It's a great bot, except that you are restricted to the CF problemset. That's why I wrote a small bot that can host a lockout-style contest with problems from Atcoder. It's pretty basic right now, but I will be working on it once the exams are over. Any feedback would be appreciated!
Small note: the current point scheme the bot uses is a bit odd, and for now you have to manually specify the contest -- the reason for these is that I originally wrote this for a tournament hosted on a different Discord server. However, these will be added / fixed later.