hook.snd.one
This is not so different from requestbin or webhook.site. The main difference is that hook.snd.one is much simpler. In addition, you can also listen from CURL. Just curl any URL with GET, and then all POSTs will show up in your terminal.
hook.snd.one also supports the browser's EventSource API, meaning it can be used to push messages from back-end to front-end in real time. The original purpose of this project was just to inspect webhooks, but I've since used it as a signalling server for WebRTC in another project. I'm pretty happy with how versatile this ended up.
This project is written in Rust using Hyper with minimal supporting libraries. The live deployment serves HTTPS requests directly using Rustls with no load balancer. This makes it easier to serve indefinitely running requests.