Although ngrok is clearly the leader at the moment, I've used Localtunnel.me in the past. There was a HN discussion about it (including some even more niche alternatives) here: https://news.ycombinator.com/item?id=7585056
It also has an incredibly useful debug console for HTTP(S) which allows you to inspect requests as they come in, its absolutely priceless when working on webhooks.
Why is that useful? Doesn't your web app or web framework already log requests?
It logs the headers and request body along with the response for every single route. This means if the server sending you a webhook changes routes, or sends some extra content or does something unexpected, you have immediate visibility into it and can replay the request with a single click.
Pretty nifty.
Most of the time request bodies do not get logged, because they often contain sensitive information.
The logging in ngrok also comes with a "replay request" button, which is very nice when you're testing webhooks that are a pain to fire.
Is this something like ISA Server does? I've been looking for something like that without the price tag and this seems it!
Yes. Well a part of what ISA does/did. As you probably already know ISA is a bit more than just a reverse proxy.