Somewhat related to my https://requesthub.xyz/, but both face the same problems:

- they must ensure high availability if they are to be expected to be used in production system, which is difficult

- they must offer some guarantees (or some form of custom domain thing + open-source), because if someone points all his webhooks to an external domain and that stops working in some months nobody will be happy

- I pretty much doubt anyone is going to pay for a simple service like this