As this is HN, to the authors, if they're reading this -- I know you may be getting some pretty critical feedback here (hopefully it's useful!) but I will say this would have handily solved an 8 figure problem for me at a previous company. There are a lot of companies where scheduling appointments in many ways /is/ the product -- being able to have good open source tooling for appointment scheduling is worth its weight in gold. I would definitely have sprung for something like this if it was available in, oh, 2017. Keep going!